336 PEOCEEDIKGS OF UNITED STATES NATIONAL MUSEUM. 



it is probably tlie remuant of a polar colony, like that in the Gulf of 

 Lyons. It ranges from five to one hundred and fifty fathoms. 



This species, like Cryptohranchia, has a rounded non-spu'al apex. 

 When the Arctic shores of Alaska are more carefully searched, it may 

 turn up there ; but it does not seem to be a common species anywhere. 



The name Pilidkim has been used for a stage in the larva of certain 

 invertebrates, but not as having an assured standing in systematic 

 nomenclature. I see no reason, therefore, why it should be replaced by 

 any other. It is hardly necessary to i)oiut out that it does not belong 

 even to the same family as the Tectura of most authors, though erro- 

 neously called Tectura by Adams and others. It was sent by Morch, 

 under the name of Patella rubella Fabr., to Dr. Stimpson, which led him 

 and the writer to erroneously unite that species (which is an Acmcca) 

 with the present one in 1865 and 1869. To Prof. Sars is due the credit 

 of pointing out the true place of the P. ruhclla. Clark speaks of find- 

 ing the fry entangled in the mucus of the foot, but this can hardly be 

 more than an accident. 



Suborder PEOTEOBHANCHIATA. 

 Family ACM^ID^ Cpr. 



Acmaklw Dall, 1. c. j). 237, 1S71. 



Genus ACM^A Eschscholtz. 



Acmcea Esch. Appendix to Kotzebue's New Voyage around the World (Dorpat, 1828), 

 Loudon reiirint, vol. ii, p. 350, 1830. — Dall, 1. c p. 237, 1871. Type A. 

 mitra. 



Having shown by evidence which cannot be successfully controverted, 

 that the name of Acmwa has precedence iu time of application over 

 Tecture Aud. {Tectura Gray), no apology is necessary for following the 

 lead of Forbes, Woodward, Hauley, Philippi, and Carpenter, in adojit- 

 ing the prior designation. Its very extensive synonymy will be found 

 in my paper above quoted. 



Subgenus Acm.<ea Dall ex Eschscholtz. 



Acmwa Dall, Am. J. Conch, vi, ^. 241, 1871. Type A. mitra Esch, 

 Erf/huts Jeffreys, Ann. Mag. Nat. Hist. Mar. 1877, p. 231. 

 Tectura Sars, Moll. Eeg. Arct. Nor^% p. 121, 1878. 



Acmaea mitra. 



A. mitra (Esch.) Rathke, Zool. Atlas, v, p. 18, No. 1, pi. xxiii, f. 4, 1833.— 

 Dall, 1. c. p. 241, 1871, pi. 14, f. 1. 



Hah. — Pribiloff Islands, Bering Sea, westward to Kyska in the Aleu- 

 tians, and eastward and southward to Sitka, Oregon, and the coast of 



