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 PlacipJiorella velaia Cpr., type of the subgenns, the gill-rows are as 

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

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

 fringed with long fleshy, processes. No oviduct coidd 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. Eec. MoU. i, p. 480, pi. 55, f. 2, 1854.— Gray, 

 Guide, p. 187, 1857. 



Type Chiton vestltns Sowerby. 



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

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

 nus ve pilosa, interdum porifera. 



Subgenus Amicula s. str. (Gray). 



Branchiie niedise. A. vestita Sowerby. 



Subgenus Chlamydochiion (Dall). 



Branchiie 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 j)osterior 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.) 



Symmetrogeplujrus Middendorf, Mai. Eos8. 1, p. 98, 1847. (C Pallasii Midd.) — Chenn, 



Man. i, 383, 1859. 

 Stimpsoniella Carpenter, Bull. Essex Inst, v, p. 1.^5, 1873. (C Pallasii Midd. and Em- 



efsonii Couth.) 

 Middendorfia Carpenter, MS. 1871. 



Amicula vestita. 



Chiton vestitus Sowerby, Zool. Journ. iv, p. 368, 1829; Conch. 111. f. 123, 128a 

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

 1839. 



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

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



