PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 307 



These species are known to me only by the types; they may extend 

 their range into the Alexander Archipelago. 



In PlaciphareUa velata Opr., type of the subgenus, the gill-rows are as 

 long as the foot, branchiae about twenty-five in number, widely separated 

 behind. Mantle-edge behind narrow and plain; in front produced and 

 fringed with long fleshy processes. Xo oviduct could be traced, though 

 the ovary was crowded with eggs, some of which were 0.25 mm. in length. 

 In them the embryo could be plainly distinguished. There were no fur- 

 rows for the shelly plates, but the eyes were quite prominent and the 

 cephalic lobe comprised nearly half the animal. There were no bands 

 of cilia, but the edge of the cephalic lobe was strongly ciliated. 



CRYPTOIDEA. 



Genus AMICULA Gray. 



Gray, Syn. Brit. Mus. 1840, also ed. 1842 (no description) ; P. Z. S. 1847, pp. 65, 69, 

 169.— H. & A. Adams, Gen. Rec. Moll, i, p. 480, pi. 55, f. 2, 1854.— Gray, 

 Guide, p. 187, 1857. 



Type Chiton vestitus Sowerby. 



Corpus regulare; lorica exposita parva, mucronata, seu subcordata ; 

 laminae insertionis mopaloideae, lam. sut. post, magnae; zona plus mi- 

 nusve pilosa, interdum porifera. 



Subgenus Amicula 9. str. (Gray). 



Branchiae mediae. A. vestita Sowerby. 



Subgenus CMamydocliiton (Dall). 



Branchiae ambientes. C. amiculata Pallas. 



Both groups are provided with pores bearing fasciculi of bristles of a 

 soft or horny character, and which, while often irregularly disposed or 

 even almost entirely absent (in particular individuals), have a tendency 

 to arrange themselves in two rows on each side of the median line, one 

 row behind the exposed point of the valve and another near its sub- 

 merged lateral posterior angle, on each side. The mantle is also pro- 

 vided with a coating of fine, chaffy, deciduous scales. 



Subgenus Amicula (Gray) Dall. 



Amicula Gray, 1. c. 1847. (C. vestitus Sow.) 



Symmetrogcphyrus Middendorf, Mai. Eoss. i, p. 98, 1847. (C. Pdllasii Midd.) — Chenu, 

 Man. i, 383, 1859. 



StimpsonicUa Carpenter, Bull. Essex Inst, v, p. 155, 1873. (C. PaUctsii Midd. and Em- 



ersonii Couth.) 

 Middcndorfia Carpenter, MS. 1871. 



Amicula vestita. 



Chiton vc.sdtus Sown by. Zool. Journ. iv, p. 368, 1829; Conch. III. f. 123, 128a 

 (from type-specimen), 1839; Zool. Beechey's Voy. p. 150, pi. xli, £ 14, 

 1839. 



f C. amiculatus Wood, Ind. Test. pi. 1, f. 12, 1828 (probably).— Reeve, Conch. 

 Icon. Mon. Chiton, pi. xi, f. 59, 1847, 



