640 PROCEEDINGS OF THE GEOLOGICAL society. —_ [June 22, 
moidal plates (7), with their rods (7), along the ventral margin, can 
be determined ; and some of them are in good condition. The hour- 
glass-shaped plates (£) are quite distinct, and are regularly arranged 
along the same margin; and those below the elevated portion of the 
dorsal fin are likewise in excellent order. 
No distinct traces of either the pectoral or ventral fins are left. 
The dorsal fin (a), too, is very imperfect, ? of an inch only remain- 
ing. The short anterior plates, or fulcra (a"), are pretty distinct ; 
but the merest traces are found of the narrow posterior part. The 
greater portion of the anterior division of the anal fin (4) is well pre- 
served, and the narrow posterior part (6’) is determinable throughout 
its length. The tail is much injured, but les, as in all the other 
examples, spread out, the two lobes being strongly defined. 
We have now only a few concluding words to say as to the place 
this curious fish should occupy in the classification. We know of 
no family with which it can be associated, though it undoubtedly is 
closely allied to the Pycnodonts; and of these perhaps it approaches 
most closely to Gyrodus and Microdon: but while in Dorypterus the 
head-bones are smooth, they are in most of the Pyecnodonts granu- 
lated or otherwise ornamented; and our fish likewise differs from 
them in the absence of the usual body-scales. 
The large and upward-shutting mouth, too, is not found in the 
Pycnodonts; and the apparent absence of the strong characteristic 
teeth of that group is noteworthy. Had such teeth existed in the 
fish under discussion, some trace of them would assuredly have been 
observed, since we have seen that the jaws are pretty well preserved 
in two or three of our specimens. It is probable therefore that the 
dental organs were small and inconspicuous, if they existed at all. The 
enormous development of the dorsal fin and the forward position of 
the ventrals are significant facts. The latter is particularly worthy 
of notice, especially when we consider that we have in this paleeozoic 
species the earliest thoracic fish known in the geological series. And 
further Sir Philip Egerton states, in a letter with which he has lately 
favoured us, that he “‘is not cognizant of any fish in strata older 
than the chalk having the fins thoracic or jugular.” On the whole, then, 
we confess ourselves at a loss to determine where to locate Dorypterus 
in the system. Is it not the representative of a distinct, family 
having a certain relationship to the Pyenodonts? This we must 
leave for the determination of those more conversant with ichthyology 
than we ourselves are. 
EXPLANATION OF PLATES. 
The following letters apply to all the figures of Horypterus Hoffmanni. 
a, dorsal fin; a’, narrow posterior prolongation of ditto; @’, anterior pro- 
longation, or fin-fulera of ditto; 6, anal fin; 4’, posterior, narrow prolongation 
of ditto; c, pectoral fins; c’, brachial rays; d, ventral fins; ¢, rhombiform 
seales of tail; f, fin-fulcra of ditto; g, lateral plates or vertebral spines ; g', bi- 
fureation of the inner extremity of ditto; /,lozenge-shaped plates, or areas,—the 
vertebral centres ; h’, ridge in the centre of ditto; 7, rods, or supplementary ver- 
tebral spines, in connexion with the lateral plates; 7, sigmoidal ridges ; 7’, sig- 
