338 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Acmsea virginea. 



Patella virginea Miiller, Prodr. Zool. Dan. p. 237, 1776. 

 Acmcea virginea Hanley, Br. Marine Conch, p. xxxii, 1844. 



Tectura virginea of authors. 



Acmcea virginea Dall, Am. J. Conch, vi, p. 243, 1871, q. v. 



This species extends from Iceland and Northern Norway south to the 

 Azores, but does not reach the shores of America. It ranges from low- 

 water mark to sixty fathoms. The Ancylus Gussoni of Costa, which has 

 been united with this species, belongs to the Siphonariidce. 



Subgenus Collisella Dall. 



Collisella Dall, Proc. Bost. Soc. Nat. Hist. Feb. 1871. (Acmcea pelta Esch.) 

 Acmcea Sars, Moll. Reg. Arct. Norv. p. 120, 1878. 



This group is distinguished by slight but constant external differences 

 and by dental characters from the typical Acmaeas. It comprises most 

 of the Alaskan species as well as many from other parts of the world. 



Acmaea (Collisella) pelta. 



A. pelta Esch. Rathke, Zool. Atlas, v, p. 19, 1833.— Dall, 1. c. p. 246, pi. 14, £ 

 6, 1871. 



Tectura cassis von Martens, Malak. Bliitt. xix, p. 92, pi. 3, f. 9-10, 1872. 



Hah. — Aleutian Islands and the southern coast of Alaska south and 

 cast to the Santa Barbara Islands, CaL, between or near tide-marks. 

 Five hundred and ninety specimens examined from my own collection 

 and many thousands in the field. 



The numerous names which the variations of this species have re- 

 ceived, and some account of its varietal forms, have been given by me in 

 the paper alluded to. Only one of these forms, A. pelta var. nacelloides 

 I). (1. c.) seems sufficiently constant to deserve a separate name. In the 

 examination of hundreds of these most variable shells, one's notions of 

 the characters sufficient among them to constitute a species or variety 

 become so enlarged as to receive little sympathy from those who know 

 the group in question from a few specimens on a museum tablet. Con- 

 slant field and museum experience for more than twelve years lias 

 only confirmed my conviction of the propriety of the views of Dr. Car- 

 penter, on the west coast species, which have been expressed in his 

 various publications. It is true that in selecting from simultaneously 

 published names, if he had known at first all that we now know, perhaps 

 a different selection might have seemed more judicious ; but I agree with 

 Dr. v. Martens that any change, now that those selections have become 

 history, would be most objectionable, and not to be countenanced. 



The strongly ribbed variety of A. pelta, which Dr. v. Martens has so 

 well figured, and has identified with the cassis of the Zool. Atlas, appears 

 to be the same. However, the Martensian shell (which I have repre- 

 sented by some magnificent examples) is so closely connected, specimen 

 by specimen, with others nearly smooth, that I cannot admit that it re- 

 quires or should receive a separate name, even if the identity were 



