Mr. R. Walker on Fossil Fishes of Dura Den. 79 



this case is very close, which is not altogether what we might 

 expect : we should rather have expected to find the head of that 

 genus agreeing in this respect with Glyptolismus and Osteolepis. 



There are some other specimens of Glyptolepis from Dura Den 

 in the museum, which now appear to me deserving of a more 

 particular notice than I at first thought. These fishes have 

 appeared to me for a considerable time to be only a variety of 

 H. Flemingii ; but a more careful examination of some of these 

 specimens has now convinced me that they are specifically di- 

 stinct : at least, the differences between these two forms are as 

 great as that which exists between many of our present species. 

 Upon comparing specimens of both forms, about the same size, 

 I find the following differences : — The fishes in question have the 

 head rather shorter in proportion to the whole length ; the first 

 dorsal and the ventral fins are placed an inch (in some cases 

 more) nearer the head ; the dorsal and anal fins are larger than 

 the same fins in any specimen of H. Flemingii that I have ever 

 seen ; and the scales, which will be more particularly noticed 

 hereafter, have their external sculpture much finer. 



The specimen figured in Plate II. measures 10^ inches in 

 length ; to this we may perhaps add another inch to complete 

 the caudal extremity. The head is to the whole length as 1 to 5 

 or 5^. The greatest depth of the body is halfway between the 

 termination of the head and the commencement of the first dorsal 

 fin, where it attains to 3 inches, from which it gradually tapers 

 to the beginning of the caudal fin, where it is 1| inch deep. 

 The pectoral fins are not preserved on any specimen. The first 

 dorsal fin commences six inches behind the snout ; its longest 

 rays are 1^ inch in length; the second dorsal fin is inserted 

 about an inch behind the termination of the first : this appears 

 to have been a large fin, with a round free margin ; the longest 

 rays measure 1 1 inch in length. The ventral fins are placed a little 

 further forward than the first dorsal ; but they are not in a suffi- 

 cient state of preservation, on this or any other specimen, to show 

 their exact form. The anal fin is situated under the second 

 dorsal, and terminates in a somewhat pointed extremity ; its 

 longest rays are 1^ inch in length. The tail appears to be 

 heterocercal : the lower lobe is well developed, but rather abruptly 

 truncated at its posterior margin ; its first rays originate about 

 \ inch behind the anal fin, where they are If inch in length; 

 from this point they become gradually shorter as they near the 

 distal end : the upper lobe consists of a number of short rays, 

 which form a kind of marginal fringe on the upper side of the 

 notochord. The scales are rounded, and appear to be rather 

 thin; but they have the crescentic area of tubercles on their an- 

 terior half very clearly exhibited (fig. 2). The exposed surfaces 



