338 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



Acmoea virg^inea. 



Fatella rirginea Miiller, Prodr. Zool. Dan. p. 237, 1776. 

 Acmiva vircjinea Haiiley, Br. Marine Conch, p. xxxii, 1844. 

 Teciura virginm of authors. 

 Acmwa virginca Dal], Am. J. Conch, vi, j). 243, 1871, q. v. 



This species extends from Iceland and Nortliern 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 Siphotmriidce. 



Subgenus Collisella Dall. 



CoUisclla Dall, Proc. Best. Soc. Nat. Hist. Feb. 1871. {Acmosa jtelta Esch.) 

 Acmcea Sars, Moll. Reg. Arct. Norv. j). 120, 1878. 



This group is distinguished by shght but constant external differences 

 and by dental characters from the typical Acmseas. 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, f. 



6, 1871. 

 Tectura mssis von Martens, Malak. Bliitt. xis, p. 98, pi. 3, f. 9-10, 1872. 



Hah. — Aleutian Islands and the southeni' coast of Alaska south and 

 east 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. pelf a var. nacelloides 

 D. (1. c.) seems sufdciently constant to deserve a separate name. In the 

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

 the characters sufScient among them to constitute a species or variety 

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

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

 stant field and museum experience for more than twelve years has 

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

 ,])enter, on the west coast species, which have been exjiressed 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, aiul 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, api)ears 

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

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

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

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



