Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/664

564 upwards and backwards. In front of the lower end of the suboperculum, a small but very distinct interoperculum is seen, of a triangular shape, with anteriorly directed apex. The præoperculum, which does not cover any portion of the cheek, shows a distinct upper and lower limb, the upper being nearly perpendicular, and curving round below into the lower, which, passing forwards, carries the articulation of the lower jaw considerably in front of the upper extremity of the suspensorium. The jaws are comparatively feeble, and the mouth very small. The mandible has quite a different shape from that in Palæoniscus, being, of. course, considerably shorter, and seems to form the immediate margin of the mouth only towards its extremity, which is bent a little downwards. The maxilla is especially feeble, extending only to about half the length of the mandible, and is absolutely unlike that in any of the Palæniscidæ, as it stops short just before the orbit, and ends with a rounded spatulate extremity, which overlaps the mandible considerably in front of the quadrate articulation of the latter. Mr. Kirkby makes no mention of teeth; nor have I discovered any; nevertheless it would be hardly safe to conclude that the jaws were edentulous. The branchiostegal rays are few in number, about seven on each side; the posterior ones are rather long, narrow, and gently curved; but they become rapidly shorter in front. In one specimen, compressed upon its back, a space is seen just behind the symphysis of the mandible, and in front of the branchiostegal rays of each side, which was probably occupied by a large median "jugular" as in Dapedius, Engnathus, &c, and in the recent Amia. The bones of the cranium proper are not well seen, owing to their delicacy, and to the crushing which they have undergone; the ethmoidal region is usually wanting or undecipherable as to its component parts. The frontals are almost always distinct as two well-marked roof-bones, broader behind than before, their outer margins being excavated in front for the orbits. Two shorter parietals succeed the frontals behind; and there are evident traces of a squamosal plate on the outer side of each parietal, above the suspensorial articulation, though the operculum is usually crushed down over this region of the skull. There are faint traces of small plates completely surrounding the orbit, which was placed nearly right over the articulation of the lower jaw instead of being considerably in front of it as in Palæoniscus. Traces also of the palatoquadrate arch are seen in many specimens; but it is hardly possible to make out its constituent bones; a well-marked quadrate, however, is distinct enough. The direction of the suspensorium is undoubtedly considerably forwards as well as downwards.

Of the elements of the shoulder-girdle, the posttemporal and supraclavicular are so generally covered and obscured by the opercular bones that a description of them is hardly possible. The clavicle, however, is usually well seen, and differs greatly from that in the Palæoniscidæ. It is a comparatively slender bone, bent forwards at a very obtuse angle about its middle; the lower extremity is pointed and comes in contact with its fellow of the