BRITISH FOSSILS. 



Decade IX. Plate III. 



PACHTCORMUS LATIPENNIS. 



[Genus PACHYCOBMUS. Agassiz. (Sub-kingdom Vertebrata. Class Pisces. 

 Order Goniolepidoti. Family Sauroidei. Sub-family Sauroidei homocerci. 1st Group, 

 tail forked.) Body deep ; vertebrae normal ; pectoral fins large ; dorsal fin opposite the 

 ventral fins ; scales thin.] 



Pachycormus latipennis. Agassiz. Poiss. Foss. vol. 2. pt. 2. p. 114. 



In detailing the generic characters of his genns Pachycormus, 

 Professor Agassiz remarks that the dorsal fin is situated opposite 

 to the interspace between the ventral and anal fins. This is 

 strictly the case in the genera Oxygnathus and Cosmolepis. In 

 SauTopsis the dorsal fin is opposed to the anal fin. In Eugnathus 

 the large dorsal is inserted opposite the ventral fins, and extends 

 backwards as far as a point coincident with the commencement of 

 the anal fin. In Caturus the dorsal fin is opposed to the ventral 

 fins, and in Pachycormus its position is intermediate between that 

 of the like fin in Caturus and Eugnathus. The first ray is imme- 

 diately over the insertion of the ventral fins, and the after part of 

 the fin stretches a short distance over the interspace between these 

 fins and the anal fin. Of the predacious ganoid fishes of the Liassic 

 period, the Pachycormi form an important group, well charac- 

 terized by their short and deep form, and the delicacy of their 

 scales, features which contrast powerfully with the lanceolate shape 

 and solid scales of the associated Eugnathi. Professor Agassiz has 

 only described four species in the Poissons Fossiles," but he 

 notifies by name several other species as worthy of more detailed 

 examination. Of these the subject I have selected for this article 

 is one of the best characterized, although the specimens hitherto 

 brought to light show only the anterior portion of the fish. 



Description. — Of three specimens under notice referable to this 

 species, I select for description the only one seen by Professor 

 Agassiz, and which is therefore the type of the species. It com- 

 prises the head, a portion of the scapulocoracoid arch, the pectoral 

 [ix. iii.] 9 D 



