Perkins.] 156 [November 3, 



MEASUREMENTS. 



Length of shell 52 mill. Breadth 29 mill. Height 21 mill. 

 " foot 10 " (contracted). " 5.4 " 



" palpi 12 " " 6 " 



" gills 38 " " 11 " 



Modiola Lam., 1798. 



Sub genus Br achydont es Swainson, 1840. 



Brachydontes plicatula Chenu, Man. Conch., Vol. ii, p. 155. 

 Modiola ylicatula Lam., An. sans Vert., Vol. vn, p. 22; Gould, In- 

 vert. Mass., p. 125, fig. 81 ; De Kay, Moll. N. Y., p. 184, pi. xxiv. fig. 

 258. 



Very abundant everywhere in mud, peat bogs, or on rocks above low- 

 water mark. Animal varies in color from white to salmon; mantle 

 freely open, white edged with brown, somewhat ruffled ; gills nearly 

 equal; foot short, brown, obtusely pointed, with a byssal groove; 

 palpi long, thin, finely striated, beveled on the inner side from a 

 central ridge. 



Brachydontes haniatus nobis. Myiilus hamatus Say, Am. 

 Conch, pp. 91, 204, pi. 1, 1822; De Kay, Moll. N. Y., p. 183. 



Shell very much incurved and contracted at the beaks, which are 

 acute, and directed a little outward; surface covered with numerous 

 fine ribs about the same width as the spaces between, more numerous 

 anteriorly; lines of growth distinct, especially on the ribs, making 

 them slightly cancellated; byssus short and thick, shell depressed 

 about the byssal opening; color dark brown or nearly black, light- 

 est on the ribs and towards the ventral margin; inside dark purple, 

 shading to white on the edge. Animal with mantle open, edge 

 double, whitish, mottled with numerous reddish brown spots, and 

 blackish on the edge, gills light yellow, the right a little longest, ob- 

 tusely pointed; foot orange, cylindrical, pointed, grooved; palpi 

 slender, beveled on the inner surfaces from a median ridge, striated. 

 This shell, described by Mr. Say from the Gulf of Mexico, occurs in 

 abundance on southern oysters, which are planted here; whether it 

 is naturalized is doubtful. An examination of the animal has led me 

 to consider it a Modiola rather than a Mytilus. It varies greatly in 

 form from being more than twice as long as broad, to about the same 

 length and breadth. The largest specimen I have seen is sixty six 

 mill. (2.6 in.) long and thirty seven mill. (.45 in.) broad. 



