1869.] 149 [Perkins. 



PETRICOLID^. 



Petricola Lam. 



Petricola pholadiformis Lam., An. sans Vert, Vol. vi, p. 

 150; Say, Am. Conch., p. 222, pi. lx, fig. 1, 1834; Gould, Invert. 

 Mass., p. 63; De Kay, Moll. N. Y., p. 228, pi. cxxviii, fig. 282. 

 Petricola for nicata Say, Am. Conch., p. 106. 



Abundant in clay, peat bogs, old timber, etc., near high water. 

 Animal white ; mantle closed in front, thickened along the closed 

 edge; gills long, rather narrow, yellow; foot when expanded broad 

 and short, triangular, pointed in front and slanting to a point behind, 

 grooved: palpi triangular, siphons united for about a fifth of their 

 extended length, after that distinct, diverging, tapering,— ventral long- 

 est; openings fringed, the ventral siphon having six long incurved 

 papillae, which are fringed on the upper surface by a row of small 

 papillae on each side, which are again in like manner fringed, alter- 

 nating with, and a little outside of, these are six somewhat smaller, 

 and outside of these another row of much smaller papilla? ; these two 

 latter rows are slightly fringed ; the dorsal siphon has inside a few 

 large, simple papilla?, and outside of these numerous smaller ones. 

 The animal is quite active in its movements. 



MEASUREMENTS. 



Length of shell 43.6 mill. Breadth 15.6 mill., convex 14.4 mill. 



" vent, siphon 62 " " 4.6 " at base, 3.2 at tip. 



u dor# u 4 5 c< u 5 u u 2.4 " 



" foot 10.6 " (extended). " 14 " 



« gills 23 " " 9 " 



" palpi 9.4 " 4 " 



Petricola dactylus Sby., 1834; Say, Am. Conch., p. 222, pi. lx; 

 Gould, Invert. Mass., p. 65, fig. 41; De Kay, Moll. N. Y., p. 228, pi. 

 xxviii, fig. 283. 



Not as common as the preceding, and seems to live in deeper water, 

 as I have not found it living with it, but only dead shells on the 

 beach. It is often larger and stouter than P. pholadiformis, and is, I 

 believe, only a variety of it. 



