New York, July 24, 1917. No. 46 



OPFjl 



Published to advance the Science of cold-blooded vertebrates 



ON THE DIFFERENTIAL CHARACTERS 



BETWEEN MUSTELUS HEM /EI AND 



MUSTELUS CALIFORNICUS. 



Mustelus henlei (Gill) is not commonly recog- 

 nized on our coast, being passed over as Mustelus 

 califofnicus which it strikingly resembles. 



The fact that these two forms have been consid- 

 ered under separate genera, is perhaps somewhat re- 

 sponsible for their being confused by collectors. One 

 naturally looks for greater differences than those that 

 exist between these two, in species belonging to sep- 

 arate genera. Should the future, however, show that 

 the young of Mustelus henlei is without the so-called 

 placenta, it must perforce be considered generieally 

 different from Mustelus califomicus. 



The character of the teeth has been considered 

 of sufficient weight for referring these species to dif- 

 ferent genera, but the dental differences between 

 them are so small that a lens is necessary to distin- 

 guish them. The slight basal denticle in Mustelus 

 henlei is not present on all of the teeth, and sometimes 

 there is a slight blunt suggestion of this denticle in 

 Mustelus califomicus. 



The distinguishing characters between these spe- 

 cies is here pointed out hoping that the easy recogni- 

 tion and separation of the species may lead to a bet- 



