NATURAL SCIENCES OP PHILADELPHIA. 259 



when, as in the case of Carcharias griseus* of Mr. Ayres, the generic position i6 

 not only assumed, but the characters forced to agree with it, tyros might be 

 readily misled, and only knowledge of correlation of essential characters will 

 enable the scientist to arrive at correct conclusions. As I have had the power 

 of examining Odontaspidoids from the same neighborhood which agree, in fa- 

 mily characters, with those species described by scientilic naturalists, and 

 which essentially agree in other respects with Mr. Ayres' description, I identify 

 them with bis species without hesitation, although I cannot adopt the name, 

 since it had received two others previously. I may add that its true relations 

 have been appreciated by both Messrs. Desor and Storer. 



As already intimated, this contribution must be considered rather as an ex- 

 position of our present ignorance of the species, than the embodiment of the 

 correct nomenclature. It is not too much to say that the titles of half the spe- 

 cies to their names require to be confirmed. Although I have seen more or 

 less of most of these species, the want of opportunity to compare them with 

 others, and the critical nature of the characters distinctive of species in this 

 order, forbid the idea of correctness in every instance. As, however, much good 

 may often be done by the mere exposition of our deficiencies, this article is 

 submitted with the hope that it may at least excite investigation. 



The synonymy of the American forms is alone introduced. 



I. Pectoral fin with the base entire in front.., SQUALL 



A. Anal fin present. 



tt. Caudal lunate ; tail keeled on one side Lamnoid/e. 



ut. Caudal with the upper lobe much elongated. 

 0. Branchial apertures entirely in front of 



pectorals Odontaspidoid.*. 



00. Branchial aperture behind above pectoral. 

 y. Caudal exceedingly long. Eyes with- 

 out nictitant membrane AlopkcoidjB. 



yy. Caudal moderately elongated. Eyes 

 with nictitant membrane. 



Head laterally produced Cestraciontoid.*. 



Head normally formed Galeorhinoidje. 



AA. Anal fin obsolete. 



Dorsals each armed in front with spine Spinacoid^s. 



Dorsals unarmed ScymnoidjE. 



II. Pectoral fin with with the base cleft in front RHIN^E. 



"Rhinoid*. 



LAMNOIDM, Mull, and Henle. * 



CETORUININJE Gill. 



CETORHINUS Blainv. 



Tetroras Raf., 1810 (desc. and name erroneous.) 

 Selache Cuv., 181 7. 

 Selachus Yarrell. 



Cetorhinus maximd8 Blainv. 



Squalus maximns (L.) Fab., F. G. 130. Mit., Tr. N. Y. i. 486. 

 Squalus elephas Des., Journ. Ac. ii. 350. 

 Squalus rhinoceros Mit, 1828 (fide DeKay.) 

 Squalus (Selache) maximus Rich., F. B. iii. 291. 

 Squalus (Selache) elephas Storer, Rep. 407. 



* The figure of this species, like the description, is thoroughly unreliable; it is better, however, 

 than that of the Myliobalis bispinoms, in which more attention appears to have boon paid tv th* 

 delineation of mathematical figures and lines tban to the representation of nsture. 

 (See Boston Journal N. H., iv., pi. 13.) 



1864.] 



