500 Memoir Sears Foundation for Marine Research 



Key to Genera 



I a. Rear end of base of ist dorsal over or posterior to origins of pelvicsj interspace between 

 1st and 2nd dorsals shorter than between 2nd dorsal and caudal. 



Isistius Gill, 1864, p. 508. 

 lb. Rear end of base of ist dorsal considerably anterior to origins of pelvics; interspace 

 between ist and 2nd dorsals considerably longer than between 2nd dorsal and caudal. 

 2a. Lower teeth erect, triangular, nearly symmetrical, serrate. 



Dalatias Rafinesque, 1810, p. 500.^ 

 2b. Lower teeth strongly asymmetrical with cusps directed outward, not serrate, their 

 outer margins notched. 

 3a. First dorsal larger than 2nd, its apex angular 5 tip of pectoral angular. 



H eteroscymnus Tanakz, 1912. 



Japan. 



3b. First dorsal at least no larger than 2nd, its apex rounded; tip of pectoral 

 rounded. 



4a. Second dorsal only about as large as ist; snout in front of mouth about 

 V2 as long as from eye to origin of pectoral. 



Somniosus Lesueur, 1 8 1 8, p. 514. 

 4b. Second dorsal considerably larger than ist; snout in front of mouth 

 nearly or quite as long as from eye to origin of pectoral. 

 5a. Second dorsal twice as long at base as ist dorsal, or more; ist dorsal 

 with a spine either partly free or entirely hidden in the skin. 



Euprotomicrus G'dl, 1864.^ 

 Indian Ocean; Philippines; New 

 Zealand; Pacific between Hawaii 

 and California; Madeira. 



5b. Second dorsal not more than 1V2 times as long at base as ist; ist 

 dorsal without spine. H eteroscymnoides Fowler, 1934. 



Natal, South Africa. 



Genus Dalatias Rafinesque, 1 8 10 



Dalatias Rafinesque, Carratt. Gen. Nuov. Sicil., l8lo: lO; type species, D. sfarofhagus Rafinesque, 1810, 

 equals Squalus licha Bonnaterre, 1788, designated by Jordan, Tanaka and Snyder, 1913.^ 



1. Including Pseudoscymnus Herre, 1935. The differences in the denticles, cited by Herre (Copeia, 1935: 1^4), do 

 not seem sufficient for generic, and perhaps not even for specific, separation; see p. 501. 



2. Including Squaliolus Smith and Radcliffe, 1912. 



3. Jordan, Tanaka and Snyder's (J. Coll. Sci. Tokyo, jj, 1913; 22) designation of sparof/iagus Rafinesque, 1810, 

 as the type of Dalatias is not invalidated by Swainson's (Nat. Hist. Fish. Amphib. Rcpt., t, 1838: 160) acciden- 

 tal (?) limitation of that genus to D. nocturnus alone in one connection, for on an earlier page (129) in the same 

 publication Swainson included D. sfarofhagus Rafinesque in it as well. Therefore, Jordan and Evermann's 

 (Genera Fish., 1, 191 7: 77) subsequent designation of nocturnus Rafinesque, 18 10, as the type species is not 

 tenable. For the rather confused history of the case, see Gill (Proc. U.S. nat. Mus., 18, 1896: 191), who arrived 

 at the conclusion that Dalatias is a synonym of Squalus, hence that the correct generic name for the shark now 

 under consideration is Scymnorhinus Bonaparte, 1846, 



