Page:Encyclopædia Britannica, Ninth Edition, v. 12.djvu/704

686 686 ICHTHYOLOGY [CLASSIFICATION. forwards, but not grown to the head. Gill-openings rather wide, lateral, partly covered by the base of the pectoral. Spiracles wide, behind the eyes. Teeth conical. One genus only: the &quot;Angel-Fish,&quot; or &quot;Monk-Fish&quot; (Rhino, squat ina), which approaches the rays as regards general form and habits. Extinct forms, closely allied to the &quot;Angel-Fish,&quot; are found in the Oolite, and have been described as Tliaumas. The Carboniferous genus Orthacanthus may have been allied to this family, but it was armed with a spine immediately behind the head. Family 10. Pristiophoridce. The rostral cartilage is produced into an exceedingly long, flat lamina, armed along each edge with a series of teeth (saw). These sharks so greatly resemble the common saw-fishes as to be easily confounded with them, but their gill-openings are lateral, and not inferior. Only one genus is known, Pristiophorus, which occurs in the Australian and Japanese seas. Squaloraia, from the Lias, is supposed to have its nearest affinities to this family. B. Batoidei, Rays. Family 1. Pristidce. The snout is produced into an exceedingly long flat lamina, armed with a series of strong teeth along each edge (saw). One genus only : Pristis (Saw-Fishes). Family 2. Ehinobatidce. Tail strong and long, with two well- developed dorsal tins, and a longitudinal fold on each side ; caudal developed. Disk not excessively dilated, the rayed portion of the pectoral tins not being continued to the snout. Teeth obtuse, granular, the dental surfaces of the jaws being undulated. Genera : Rhytichobatus, lihinobatus, and Trygonorhina. Fossil : Spathobatis and Trigorhina. Family 3. Torpedinidce ((Electric Rays). Trunk a broad, smooth disk. Tail with a longitudinal fold on each side ; a rayed dorsal tin is generally, and a caudal always, present. Anterior nasal valves confluent into a quadrangular lobe. An electric organ composed of vertical hexagonal prisms between the pectoral fins and the head. Genera : Torpedo, Narcine, Hypnos, Dwcopyge(fr6iu Peru), Astrape, and Temera. A large fish, with the general appearance of a torpedo, has been found at Monte Bolca ; and Cyclobatis, from the Upper Cretaceous Limestone of Lebanon, is probably another extinct repre sentative of this family. Family 4. Rniidce. Disk broad, rhombic, generally with asperities or spines ; tail with a longitudinal fold on each side. The pectoral fins extend to the snout. No electric organ ; no serrated caudal spine. Genera : Raia (Rays and Skates), Psammobatis, Sympterygia, Platyrhina. Fossil : Arthroptcriis. Family 5. Trygonidce.Uhe pectoral fins are uninterruptedly continued to, and are confluent at, the extremity of the snout. Tail long and slender, without lateral longitudinal folds ; vertical fins none, or imperfectly developed, often replaced by a strong serrated spine. Genera : Urogymnus, Trygon (Sting- Rays), Urolophus, Ptero- platea. Family 6. Myliobatidce( &quot;Devil-Fishes,&quot; &quot;Sea-Devils,&quot; or &quot;Eagle- Rays&quot;). The disk is very broad, in consequence of the great de velopment of the pectoral fins, which, however, leave the sides of the head free, and reappear at the extremity of the snout as a pair of detached (cephalic) fins. Viviparous. Genera : Myliobatis, Aetobatis, Rhinoptera, Dicerobatis, Cerato- ptcra. Fragmentary portions of their tessellated dentition are com mon in Tertiary formations. SUBORDER II. Holocephala. One external gill-opening only, covered by a fold of the skin, which encloses a rudimentary cartila ginous gill-cover ; four branchial clefts within the gill-cavity. The maxillary and palatal apparatus coalescent with the skull. This suborder is represented in the living fauna by one family only, Chimceridce ; it forms a connecting link with the following order of fishes, the Ganoids. In external appearance, and as re gards the structure of their organs of propagation, the chimseras are sharks. The females are provided with &quot;claspers&quot; in connexion with the ventral fins, and the ova are large, encased in a horny capsule, and few in number ; there is no doubt that they are im pregnated within the oviduct, as in sharks. The males are pro vided with a singular erectile appendage, spiny at its extremity, and received in a groove on the top of the head. On the other hand, the relations of the chimseras to the Ganoid, and, more especially, to the Dipnoous type become manifest, in their notochordal skeleton and continuity of cranial cartilage. The spiiw in front of the first dorsal fin is articulated to the neural apophysis, and not merely im planted in the soft parts ; it is immovable as in sharks. A cartila ginous operculum makes its appearance, and the external gill-opening Is single. The dentition is that of a Di|&amp;gt;noid, each &quot;jaw&quot; being armed with a pair of broad dental [dates, with the addition of a pair of smaller cutting teeth in the upper &quot;jaw.&quot; Fossils of similar dental combination are not rare in strata commencing with the Lias and the bottom of the Oolitic series ; but it is impossible to decide in every case whether the fossil should be referred to the Holocephalous or the Dipnoous type. According to Newberry, Chimaeroid fishes commence in the Devonian with lihynchodus, the remains of which were discovered by him in Ohio. Undoubted Chimreroids are Elasmodus, Psaliodus, Ganodus, Ischyodus, Edaph- odon, and Elasmognathus, principally from Mcsozoic and Tertiary formations. Very similar fossils occur in the corresponding strata of North America. A single species of Oallorkynckus has been dis covered by Hector in the Lower Greensand of New Zealand. The living chimseras are few in number, and remain within very moderate dimensions, probably not exceeding a length of 5 feet, inclusive of their long filamentous, diphyeercal tail. They are referred to two genera, Chimcera and Cullorhynchus. ORDKR II. Ganoidci. Skeleton cartilaginous or ossified. Body with medial and paired fins, the hinder pair abdominal. Gills free, rarely partially attached to the walls of the gill-cavity. One external gill-opening only on each side ; a gill-cover. Air-bladder with a pneumatic duct. Ova small, impregnated after exclusion. Embryo sometimes with external gills. To this order belong the majority of the fossil fish remains of Palaeozoic and Mesozoic age, whilst it is very scantily represented in the recent fauna, and evidently verging towards total extinction. The knowledge of the fossil forms, based on mere fragments of the hard parts of the body only, is very incomplete, and therefore their classification is in a most unsatisfactory state. In the following list only the most important groups will be mentioned. 1 Eight suborders may be distinguished at present. SUBORDER I. Placoderini. Extinct. The head and pectoral region of the body encased in great bony sculptured plates, with dots of enamel ; the remainder of the body naked, or with ganoid scales ; skeleton notochordal. Comprises the oldest vertebrate remains, from Devonian and Car boniferous formations. Genera : Pterichthys, Coccostens, Dinichthys, Cephalaspis, Auchen- aspis, Didymaspis, Pteraspis, Scaphaspis, Cyathaspis, Astrolepis. SUBORDER II. Acantliodini. Extinct. Body oblong, compressed, covered with shagreen ; skull not ossified ; caudal fin heterocercal. Large spines, similar to those of Chondropterygians, in front of some of the median and paired fins. The spines are imbedded be tween the muscles, and not provided with a proximal joint. Genera : Acanthodes, Ckiracanthus, from Devonian and Car boniferous formations. SUBORDER III. Dipnoi. Nostrils two pairs, more or less with in the mouth ; limbs with an axial skeleton. Lungs and gills. Skeleton notochordal. No branchiostegals. Family 1. Sircnidce. Caudal fin diphyeercal ; no gular plates ; scales cycloid. A pair of molars, above and below, and one pair of vomerine teeth. Genera : Lepidosiren and Ccratodus. Lepidosiren (including Protoptcrus) has the body eel-shaped, with one continuous vertical fin. The limbs are reduced to filaments. Vomerine teeth conical, pointed. Each dental lamina or molar with strong cusps, supported by vertical ridges. Conns arteriosns with two longitudinal valves. Ovaries closed sacs. Two species are known : L. paradoxa, from the system of the river Amazon, and L. (Protop! erus) annectens, which abounds in many localities of the west coast of Africa, is spread over the whole of tropical Africa, and in many districts of the central parts forms a regular article of food. Ceratodus has the body elongate, compressed, with one continu ous vertical fin. The limbs are paddle-shaped, with broad, rayed fringe. Vomerine teeth incisor-like ; molars with flat, undulated surface, and lateral prongs. Conus arteriosus with transverse series of valves. Ovaries transversely lamellated. Two species, C. forstcri and G. miolepis, are known from fresh waters of Queensland. The specimens obtained hitherto have come from the Burnett, Dawsoh, and Mary rivers, some from the fresh waters of the upper parts, others from the lower brackish portions. The fish is said to grow to a weight of 20 ft&amp;gt; and to a length of 6 feet. Locally, the settlers call it &quot;Flat-head,&quot; &quot;Burnett-Salmon,&quot; or &quot; Dawson-Salmon,&quot; and the aborigines &quot; Barramunda,&quot; a name which they appear to apply also to other large-scaled freshwater fishes, as the Osteoglossum leichardti. In the stomach there is gene rally foxmd an enormous quantity of the leaves of plants growing on the banks of rivers, evidently eaten after they had fallen into the water and when in a decomposing condition. The flesh of the fish is salmon-coloured, and is much esteemed as food. The barra- munda is said to be in the habit of going on land, or at least on mud-flats; and this assertion appears to be borne out by the fact 1 For a study of details we have to refer to Agassiz, foissons Fossiles ; Owen, Palcenntoloyy, Eclin., 1861, 8vo; Huxley, &quot; Preliminary Essay upon tlie Systematic Arrangement of the Fishes of the Drvonian Epoch,&quot; in Mem. Geolog. Survey, December 10, 1861, and &quot; Illustrations of the Structure of Crossopteryffiaii Ganoids,&quot; ibid., December 12, 1866; Traquair, 77 e Ganoids of th British Carbuni- ferous Formations, part i!, &quot; Palseoniscidse,&quot; Talseontocr. Soc. Lond., 1877; and &quot; On the Structure and Affinities of the Flatysomidue,&quot; in Trans, hoy. Soc. Edin. vol. xxix.