626 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [June 22, 
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 
Minster, 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 descrip- 
tion 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 imper- 
fect state of the tail in the specimen examined ; but in those which 
we have investigated this fin is very well preserved in three indivi- 
duals, 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 Miinster says of his Platysomus Althausi (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 with- 
out 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 re- 
semblance in its external form to Platysomus qubbosus, 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 com- 
parison 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 
