Fam. 6Q.] NATURAL HISTORY SOCIETY. 145 



sharp; operculum horny, subspiral ; yellowish-brown, usually 

 covered by a dark green pigment. Animal dusky-brown and 

 drab; motions very active. L. 4 ; D. 2 ; An. 30°; Wh. 5; Ap. 

 J. — N. J. and north. Common on sea-weeds near shore, and in 

 brackish water. 



Family 65. ADEORBID/E. 



A small family of depressed almost disk-shaped shells. 

 1. Skenea, Flemg. 



Shell minute, depressed, nearly discoid a 1, few-whorled ; peris- 

 tome entire, round ; operculum multispiral. 



1. Skenea plannrbis, Fai)r. Shell minute, flat, slightly convex 

 above, broadly concave below, forming a deep umbilicus showing 

 all the whorls ; whorls smooth ; aperture circular, with a sharp 

 lip ; operculum multispiral. Light horn-color. Length of 

 axis I; D. IJ; An. 130°; Wh. 3; Ap. f.— New York and north. 

 Common under stones at low water. 



Family 66. CALYPTR/EID/E. 



Shell flat or boat-shaped, with the apex more or less spiral ; 

 interior with a shelly process or shelf, variously shaped, to 

 which the adductor muscles are attached. Animal with a dis- 

 tinct head ; muzzle lengthened and split, but non-retractile ; eyes 

 on the external bases of a pair of tentacles. 



The bonnet-limpets adhere to stones and shells; most of them 

 appear never to quit the spot on which they first settle, as the 

 margin of the shells becomes adapted to the surface beneath, 

 while some wear away the space below their foot, and others 

 secrete a shell base. 



* Shell conical ; partition cup-shaped /. Crueibulum. 



* vShell oblong, flat or convex ; partition nearly flat 2. Crepidula. 



1. Crucibulum, Schum. 



Shell conical, with an internal, cup-shaped plate attached on 

 one side to the wall of the shell. 



1. Crucibulum striatum^ Say. Cup and saucer Limpet. Shell 

 moderately solid, conical with numerous, equidistant, elevated, 

 radiating lines; aperture circular; summit smooth, obtusel}' 

 pointed, inclined toward the left side and posterior end ; inter- 

 nal, cup-shaped partition attached at one side and terminating 

 near the inner apex of the shell. White to waxy-yellow. 



