S. I. Smith — Crustaceans of the Atlantic Coast. 



81 



cimeiis examined, all the males 28"'"' or less in length have Avell-devel- 

 oped rostral teeth and a distinct spine (the pterygostomian) at the 

 inferior angle of the anterior margin of the carapax, and in these 

 characters agree fully with the female. In all the specimens much 

 above 30""" in length the pterygostomian spines are small, rudiment- 

 ary or wanting, though they do not seem to disappear wholly at any 

 particular size of the individual. The disappearance of the dorsal 

 teeth of the rostrum is still more irregular and is evidently a charac- 

 ter peculiar to, but not characteristic of, the adult male. There are 

 often very rudimentary teeth present which could not be discovered 

 without the aid of a leuse, and the gradation between the forms in 

 which they are well-developed and those in which they are Avholly 

 wanting is most complete. That the form of male with edentulous 

 rostrum and without pterygostomian spines has no claim to be 

 retained as a species is conclusively shown, (l) by the complete gra- 

 dation in these characters between this form and the origiual polaris- 

 form, (2) by the fact that one of the characters may exist without 

 the other in the same individual, and (3) by the negative evidence 

 that there is no corresponding female form. 



The following tabulation of the character of the rostral teeth and 

 the pterygostomian spines, together with the length of the individual 

 and the rostral formula, in a series of specimens selected from a much 

 greater number, exhibits some of the variations. The letters indicat- 

 ing the localities correspond with those in brackets under the distri- 

 bution of the species given above. 



Pterygostomian spine. 

 Well-developed. 



Small. 



February. 1879. 



