338 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



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Acmaea virginea. 



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

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

 Tectura virginea of authors. 

 Acrrnxa virginea DaU, Am. J. Couch, vi, p. 243, 1871, q. v. 



This species extends from Iceland and Nortliem 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 Sip1ionariid{e. 



Subgenus Collisella Dall. 



Colliscllu Dall, Proo. Bost. Soc. Nat. Hist. Feb. 1871. {Acmna jteltti.'EBch.) 

 -Icmwa 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 (CoUisella) pelta. 



J. iielfa Esch. Kathke, Zool. Atlas, v, p. 19, 1833.— Dall, 1. c. p. 246, pi. 14, f. 



6, 1871. 

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



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

 ea«t 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 accotint of its varietal forms, have been given by me in 

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

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

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

 the characters sufficient among them to constitute a species or variety 

 become so enlarged as to receive little sympathy fi'om those who know 

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

 stant field and museum exi:>erience for more than twelve years has 

 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 

 vaiious pubhoations. 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 agTec with 

 Dr. V. Martens that any change, now that those selections lla^-e become 

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



The strongly ribbed variety of J^.^eZto, which Dr. v. Martens has so 

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

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

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

 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 



