MARINE MOLLUSCA OF THE UNITED STATES. 95 
upon differences in the animals which do not appear to me to be 
of generic value. 
1. P. ca@ca, Muller. Fig. 192. 
Zool. Danica, i. 45, t. 12, f. 1, 2,3. 1788. 
Patella candida, Couthouy, Am. Journ. Science, xxxiv. 217. 1838. 
Shell small, conical, with numerous minute revolving ribs crossed 
by fine concentric lines, giving the surface under the lens the ap- 
pearance of network; summit nearly central; margin slightly 
scolloped by the termination of the ribs. White. 
Length 8.75, height 2.5 mill. 
New England, northwards. (Hur.) 
2. P. TESTUDINALIS, Miller. Fig. 193. 
Prod. 237. 
Patella tessellata, Miill., Zool. Dan. Prodr., iii. 2868. 1788. 
Patella Clelandi, Sowerby, Trans. of Linn. Soc., viii. 621. 
Patella virginea, Miill., Zool. Dan. Prodr., iii. 2867. 1788. 
Patella amena, Say, Journ. Philad. Acad. ii. 223. 1822. 
Patella clypeus, Brown, Brit. Conch., t. 37, f. 9,10. 1827. 
Lottia antillarum, Sowerby, Conch., Man. f. 281. 
Shell oblong-oval, frequently with a calcareous deposit, under 
which we observe numerous radiating lines, which are crossed by 
minute concentric wrinkles. Margin entire, acute; apex behind 
the middle, and turning towards the short end. Whitish or 
greenish, with brown bands, frequently interrupted, forming 
square tessellated spots; within bluish-white, etc., with an apicial 
brown spot and marginal band. : 
Length 20 to 38, width 12 to 20 mill. 
Northern Coast. (Hurope.) 
3. P. ALvEus, Conrad. Fig. 194. 
Journ. Philad. Acad., vi. 267, t. 11, f. 20. 1831. 
Shell oblong, sublinear, elevated, thin, pellucid, with fine radiat- 
ing striz and fine concentric lines; sides nearly straight; apex 
not central, pointing to the short end. Whitish, with reddish- 
brown spots and lines, visible within. 
Length 7.5 to 12.5, width 5 to 7.5 mill. 
New England. 
This is doubtfully distinct from testudinalis. 
