712 DR RAMSAY H. TRAQUAIR S DESCRIPTION OF 



in which the superior maxilla is formed of one piece, and the branchiostegal rays 

 are many and enamelled. Here they must form a distinct sub-family of Palceon- 

 iscidw, equivalent to the " Lepidoidei heterocerci " catalogued by Sir Philip 

 Egerton in the " Quart. Jour, of Geol. Society," (vol. vi. 1850), but with the addition 

 of Pygopterus, Acrolepis, and some other allied genera, generally classed as 

 " Sauroids" the family being characterised by their wide gape, many rayed ful- 

 crated fins, and by their completely heterocercal tail, the upper border of which 

 is set with a row of imbricating V-shaped scales. 



But the last question is, whether Eurynotus is also to be considered a member 

 of the Palceoniscidce, or to be transferred to the Pycnodonts, which it resembles 

 in the rounded crushing palatal and other teeth. This question has already been 

 discussed by Sir Philip Egerton in the paper above referred to ; and the con- 

 clusion to which he there arrives, taking the form and structure of the scales and 

 fins into account, is, that Eurynotus ought to retain its place among the " Lepi- 

 doidei heterocerci." But in a paper very recently read before the Geological Society 

 of London, Dr J. Young has removed it from its old associates, and placed it, 

 together with Platysomus, the Pycnodonts, and two new genera, Amphicentrum 

 (Young), and Mesolepis (Young), in his family of Lepidopleuridce. I regret that 

 my knowledge of the last-named fishes is not sufficient to enable me to venture 

 an independent opinion as to the relations to them of Eurynotus. As regards the 

 configuration of the scales, the structure and general form of the fins, except in 

 the case of the dorsal, Eurynotus certainly bears a very strong resemblance to 

 Amblypterus and Palceoniscus. But the dentition and the shape of some of the 

 bones of the head distinguish it so much from the two last-named genera, that it 

 is not impossible, that, when we come to know more about the cranial structure 

 of Eurynotus and that of the apparently allied genus Mesolepis (Young), Dr 

 Young's ideas will be found to be substantially correct. 



Explanation of Plate XL V. 



The various bones are designated and numbered according to the nomenclature used by Professor 

 Owen in his " Lectures on Comparative Anatomy." 



Fig. 1. Pygopterus Greenockii (Agassiz), one-half natural size. 

 D, Dorsal fin ; C, Caudal ; A, Anal ; V, Ventral. 



Fig. 2. Head of another specimen seen from the side, diminished one-third. 



L, J, Lower jaw T ; N, Nasal opening ; /, Pre-coracoid plate ; g, Triangular cheek- 

 plate. 

 15, Nasal bone; 21, Superior maxillary; 22, Pre-maxillary ; 35, Operculum; 

 36, Suboperculum ; 44, Branchiostegal rays or plates; 50, Suprascapular; 

 51, Scapular; 52, Coracoid ; 73, Suborbital. 



