336 PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 



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

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



This species, like Cryptobranchia, has a rounded non-spiral 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 Pilidium 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 point out that it does not belong 

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

 neously called Tectum 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 Acmcea) 

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

 of pointing out the true place of the P. rubella. Clark speaks of find 1 

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

 more than an accident. 



Suborder PEOTEOBRANCHIATA. 

 Family ACJLEIDiE Opr. 



Acmwidw Dall, L c. p. 237, 1871. 



Genus ACMCEA Eschscholtz. 



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

 London reprint, vol. ii, i>. 350, 1830. — Dall, 1. c. p. 237, 1871. Type A. 



mitra. 



Having shown by evidence #hich cannot be successfully controverted, 

 that the name of Aemaa has precedence in time of application over 

 Tecture And. [Tectum Gray), no apology is necessary for following the 

 lead of Forbes, Woodward, Eanley, Phllippi, and Oatfptonter, in adopt- 

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

 in my paper above quoted. 



Subgenus ACMJEA Dall ex Eschscholtz. 



Acmova Dall, Am. J. Conch, vi, p. 241, 1871. Typo A. mitra Each. 

 Brginua Jeffreys, Ann. Mag. Nat. Hilt. Mar. 1877, p. 231. 

 Tectum Sars, Moll. Keg. Arct. Norv. p. 121, 1878. 



A cm sea mitra. 



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

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



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

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



