434 PROCEEDINGS OP THE GEOLOGICAL SOCIETY. [JunO 18, 



Glyptol^mus. — The specimens of this genus that I have examined 

 differ in no respect from the description given by Professor Huxley. 

 Some small specimens seem to indicate the possibility of the exist- 

 ence of more than one species ; but of this the proofs are as yet in- 

 distinct. 



PsAioiEOPLEirRON'. — The genus Phaneropleuron is very readily re- 

 cognized by the ribs being so distinctly exhibited in all specimens 

 that I have yet seen. This seems to have been occasioned both from 

 the ribs being ossified, and also from the scales being very slenderly 

 attached to the integument, and hence being seldom found on the 

 body at all, and thus the neural and haemal spines, being only 

 covered by a very thin skin, are distinctly seen, while in fishes 

 covered with firmly attached and strong, thick scales, such as Holo- 

 ptychius and the like, even had these been ossified asm Phaneropleu- 

 ron, they would have been completely hidden from view. One or 

 two scales only in any of the specimens have been found occupying 

 their proper position, many others being scattered over the surface of 

 the slab. These scales had been very thin, compared with those of 

 Holoptychius or Glyptolepis, ornamented on half the scale with rather 

 weU-marked, radiating, curved ridges, the other half having delicate 

 radiating striae. This sculpturing seems, as in many other of these 

 fishes, to vary in different parts of the body. They were of a circular 

 or, rather, elliptical form, and in a fish about fifteen inches in length 

 were about half an inch in diameter. None of the specimens that 

 I have yet examined show the under part of the head; and, in all, 

 the cranial bones are very indistinctly preserved. The opercular bone 

 seems to have been large and particularly strong, as it is well pre- 

 served in most specimens, even in those where every other portion of 

 the head is quite obliterated. What appears to have been a coracoid 

 is indistinctly preserved in some. The anal, caudal, and dorsal fins 

 seem to have been united, the dorsal having been certainly extended 

 along the posterior half of the body. On one or two specimens there 

 are indications showing the probability that this fin was continued 

 along the half of the remaining portion of the body, if not aU the 

 way to the occiput, as described in the ^ Decade.' This fin increases 

 in height posteriorly, but, instead of being truncated, appears to have 

 been rounded off posteriorly, the body of the fish gradually lessening 

 in circumference, and extending all through. The caudal fin appears 

 to me to have been almost diphycercal in character, the upper and 

 lower lobes being nearly equal in size. The ventral fin is better 

 preserved in the specimen figured in the ' Decade' than in any other 

 that I have yet seen ; it is, however, distinctly marked in one or 

 two. The pectoral fin also is preserved, although less distinctly 

 shown. These fins were very similar in character : the pectoral was 

 rather larger than the ventral ; both were acutely lobed, and had, as 

 stated in the ' Decade,' the edges fringed with delicate fin-rays. In 

 all other respects, in so far as my observation goes, they coincide 

 with the description given in the ^Decade.' Nor are there the 

 slightest grounds for the supposition that more than one species of 

 this genus exists in the Dura Den sandstones. 



