n6 POLYTROPA. 



Dr. p. p. Carpenter was the first who attempted to classify 

 the lapillus group of the West Coast of North America ; he 

 separates them as follows : 



" P. saocicola^ Val. Some varieties run into the New England 

 form of F. lapillus suffleiently nearly to justify the identifica- 

 tion; but the bulk of the specimens are easily distinguished b}' 

 the excavated columella. They pass by insensible gradations to 

 P. ostrina, Gould, which is a rare and exti-eme variety. Many 

 of the shells called P. Freycinelii b}^ Midd., are certainly refer- 

 able to this species. Some forms pass towards the true P. Frey- 

 cinetii. Desh., while others are equally close to the ver}' diti'erent 

 P. emarginala^ Desh. 



''Y^r./uscaia, Forbes. 



" Var. emarginata, Desli. 



'' Var. oslrina. GUI. 



'' /-*. canaUciiUila , \)\u'\.^^ (h'cemrnxla/a. Midd., atle-vuata, Rve., 

 analoga^ Forbes. 



" P. crispata, Chemn. = pJirala^ Mart., laclaca. Esch.. septen- 

 Irionalis, Rve.. etc." 



E. von Martens (Mai. Biatt., xix, 80, 1872) does not hesitate 

 to refer all these forms to P. lima. Martyn, but does not speak 

 of their relationship to lapilluH except as "' N. W. American 

 species of Purpura of the lapillus group." 



Doubtful Species referred to Polytropa. 



P. EXiLis, Dunker. 



Narrowly ovate, yellowish, whorls four, with a number of 

 revolving riblets and strifv, decussated by narrow growth-lines ; 

 body-whorl double the length of the spire, with three revolving 

 costulse, next whorl bicarinate, upper one unicarinate ; aperture 

 ovate; columella sinuous ; labrum thickened, erenulate. 



Length 7 mill., diam. 8 mill. 



Upol'ii. 



Not figured. Evidently a young sliell. .iiid Mi)pcars to be 

 related to P. haemastoma. 



