1869.] 123 [Perkins. 



MEASUREMENTS. 



Length of shell 28.8 mill. Breadth 26 mill. Height 19 mill. 



" foot 21 " " 19 " 



" tentacles 3.4 " 



u lobes of head 2.4 " " 2.2 " 



" branchial plume 22.6 " 



Branchial plume covered by the mantle, dark brown. The eggs are 

 laid in May. The ova cases are attached in a rosette-like cluster of 

 about thirty, by long slender filaments. The capsules are triangular, 

 thick, colorless, about two thirds filled with minute yellow ova. 

 Length four and one-fifth mill. ; breadth four mill.; thickness two and 

 four-fifths mill. Peduncle four mill. long. 



Crepidula unguiformis Lam., An. sans Vert, Vol. vn, p. 643. 

 Crepidula plana Say, Am. Conch., p. 74, pi. xliv, 1822; Gould, 

 Invert. Mass., p. 159, fig. 76; De Kay, Moll. N. Y., p. 158, pi. vii, 

 fig. 153. 



Yery common, often completely lining old shells, and also on the 

 outside. I have taken nearly two hundred from a single shell of 

 Fulgur. The young are usually found on the older ones. The lack of 

 convexity is very constant. Animal white; rostrum short, broad, 

 bilobed; tentacles short, obtusely pointed, semitransparent, white at 

 the tips; foot ovate, a little more than half as long as the shell, con- 

 cave before, auricled, round behind; ova capsules in clusters like the 

 preceding; capsules broadly triangular, thin, transparent, about forty 

 in each clustery ova light yellow, clustered about the upper edge and 

 along the sides, leaving the centre free, and usually the lower part. 

 Length two and one-fifth mill. ; breadth three mill. ; thickness one 

 and one-fifth mill. Length of peduncle four and three-fifths mill. 



These capsules are similar to those of C. fornicata, but are broader, 

 shorter, and thinner, and the ova are differently situated. Laid in 

 June. 



RISSOID^. 



Sub-Family Rissoin^e Stimps., 1865. 



Eissoa Fleming, 1814. 



Hissoa aculeus Stimps., Proc. Bost. Soc. Nat. Hist., Yol. IV, p. 

 15. Cingula aculeus Gould, Invert. Mass., p. 2G6, fig. 172; De Kay, 

 Moll. N. Y., p. 110, pi. vi, fig. 115. 



Common under stones and on akas near low water. 



