Page:Quarterly Journal of the Geological Society of London, vol. 26.djvu/864

 lower jaw, the rather large orbit, and the unusually long dorsal fin would alone be sufficient to establish this identity ; but to these points may be added the situation of the pectoral in the mid-height of the body, the curious " ribbon-shaped " process descending from behind the pectoral to the ventral margin, the abdominal rod which bounds the ventral cavity behind (not mentioned by Germar or Munster, but characteristically shown in their figures) the hour- glass-shaped processes beneath the dorsal, and the peculiar sigmoidal plates seen near the ventral margins of the posterior half of the body : these establish beyond any doubt, not only the generic, but also the specific identity of the Marl-slate with the Kupferschiefer specimens. But there are a few points in Prof. Germar's description which the more perfect state of the specimens we have had the use of enable us to correct. It will appear in the sequel that what seemed to Germar to be an internal bony skeleton is, according to our observations and opinions, also in part an exo-skeleton. The situation of the ventral fin also, which is placed in this fish under the throat and rather in advance of the pectoral fin and ventral cavity, has been overlooked by this author (for, judging from his figure, the ventral appears to be present) ; and in consequence of this oversight, he has been led to consider the anal the ventral, and the anal (which is well shown in his specimen) not to be present. Another point deserving of remark is the statement that the tail is homocercal. This idea arose, no doubt, from the imperfect state of the tail in the specimen examined ; but in those which we have investigated this fin is very well preserved in three individuals, and shows itself to be decidedly heterocercal. The size of Germar's specimen is rather less than that of three of ours ; but the dorsal fin is more perfect and more characteristically shown in the German than in those which we have before us from Midderidge.

Count Munster says of his Platysomus Althausii (Munster, Beitrage, Heft v. p. 44, tab. v. f. 2) that " the only two small individuals of this species which I saw at Mr. Althaus's are of equal size, but both without scales, so that only the skeleton of the fish is seen, an appearance very common in the lithographic slates of Bavaria, but very rare in the Kupferschiefer. One recognizes pretty clearly the very strange composition of the skeleton of this fish, which Agassiz has fully described in ' Recherches sur les Poissons Fossiles.' Only faint impressions exist of each individual.

" The individual figured (Taf. v. f. 2), which Mr. Althaus was so kind as to let me have, has at the first superficial glance some resemblance in its external form to Platysomus gibbosus, Agassiz, so that at first I thought this might be only the skeleton of a young individual of that species ; but a stricter investigation and comparison soon convinced me that it is an entirely new species.

" The body has a rounded rhomboidal, nearly ovate form. The head is disproportionately large, and occupies nearly one half of the body ; its profile from the dorsal fin to the snout is somewhat straight ; the snout much bent. The large orbit is placed high and far backwards. The faint impressions of the head-bones are