NATURAL SCIENCES OP PHILADELPHIA. 151 



Dr. Ayres then implies that it is only after several changes that I have ar- 

 rived at the conclusion regarding the generic distinction of Notanhynehus. I 

 have had two opinions, one, before seeing the species, that it was a Heptran- 

 chias of Rafinesque or Baptanchus of Miiller, accepting the views of Miiller 

 and Henle, Gray, Girard, &c., and the final one, after study of the Nisqually 

 jaw, that it was the representative of a distinct genus. For that genus I 

 have adopted Ayres' name, but by no means the ideas connected with it by 

 him. 



One statement of Dr. Ayres is especially entitled to attention, as, if cor- 

 roborated, it must effect an entire revolution in our views respecting the value 

 of dentition, and is entirely opposed to the experience of Miiller and Henle, 

 Bonaparte, Agassiz, and all others. He remarks that my description of the 

 dentition " represents the individual specimen on which it was founded ; but 

 the species is quite common here, and I find that the number and the forms 

 of the teeth vary so much that my original description, which Mr. Gill says 

 is ' equally applicable to any species of the family,' is fully as close as nature 

 will allow us to draw." It is certainly rather unfortunate for science, as well 

 as himself, that Dr. Ayres has omitted to produce proof of so remarkable a 

 discovery, as, on account of the respectability and number of the gentlemen 

 alluded to who have adopted other views, and in deference to whom reasons 

 might be assigned, it will be regarded with at least some doubt and skepti- 

 cism, notwithstanding even Dr. Ayres' assertion. It is scarcely necessary to 

 remark, that if this discovery is confirmed, Notorhynchus must be suppressed 

 and its species referred to Heptranchias ; but until such is done, it may, with- 

 out any imputation on the perfect reliability of Dr. Ayres, be retained, since 

 that learned gentleman has himself done so, notwithstanding his discovery 

 and the admission of a misapprehension in regarding its representative as 

 the type of a new genus. 



June 1th. 

 Mr. Jeanes in the Chair. 

 Seven members present. 



Mr. Gill called the attention of the members to several points in Ichthy- 

 ology and Couchology. He exhibited from the collection of the Academy a 

 specimen of a species of Percopsis obtained by Surgeon General Hammond in 

 Kansas. The differences between it and the Percopsis guttatus, Ag., of Lake 

 Superior, also exhibited, were strong ; the head is larger, (contained 3 \ times 

 in the length, exclusive of caudal ,) the dorsal is higher, (the longest ray equal 

 to 4| of length ;) the anal is also higher, (the longest ray contained six times 

 in length ;) the pectoral equals the height of the dorsal (=4| ;) the ventral 

 especially is longest, contained 5| times in the length, and its extremity covers 

 the anus, which is nearer the snout than the margin of the caudal fin. The 

 species may be named, in honor of its distinguished discoverer, Percopsis , 

 Hammondii. 



Mr. Gill remarked that, after an examination of the species of Sodis, Raf., 

 and Paralepis, Cuv., in the collection of the Academy, he was convinced that 

 the families of Paralepidoids and Alepidosauroids were most closely allied. 



Mr. Gill next referred to the history of the name Gymnotus, showing that it 

 had been originally founded solely on the Gymnotus carapus, and that even 

 after the introduction of the Gymnotus electricus into the system, the G. carapus 

 was retained as the first of the genus. The retention of the name Gymnotus 

 for the G. electricus and the bestowal of a new one on G. carapus are therefore 

 obvious infractions of the laws of nomenclature. The name Gymnotus must 

 be retained for G. carapus, and a new one given tothe Gymnotus electricus, Linn. 



1864.] 



