MAZATLAN UNIVALVES 2838 
to the right : sometimes however it is rather spiral, resembling 
C. aculeata. The deck margin generally has a more or less 
re-entrant angle in the middle. This however is sometimes 
rounded; sometimes nearly straight. ‘The sides are either 
straight or lobed. The anterior sinus is either very deep or 
scarcely perceptible. The sinuated part is sometimes callous. 
The surface of the deck is generally thin, displaying fine striz of 
growth. ‘The inner surface is either very glossy, or (under the 
microscope) most finely corrugated. The coloured lines are 
extremely variable in the same specimen, being often conspicu- 
ous when young and suddenly ending. Very young shells 
were extremely rare. The animal hollows out a place for itself 
on Patella Mexicana, &c. ; but no shelly deposit has been ob- 
served. The largest sp. measures long. 1°95, lat. 1°35, alt. °46. 
A flat sp. Fe IS 4Gr es Oo a aeolian 
A rounded, convex sp. _,, i kde” a One eae 
An elongated sp. a iY aS Oke eee 
Sp. a. Deck margin from vertex ‘77, from opposite end ‘45. 
Sp. 6. 93, ys A) 8. 
Hab.—Mazatlan ; abundant ; L’pool Col.—(C. nivea) Panama ; 
under stones near low water mark, not common; C. B. 
Adams.—(C. squama) Panama, Cuming :—do. under stones . 
and in dead shells near low water mark, not common ; 
CO. B. Adams.—(C. Lessonii) Isle of Muerte ; under stones 
at low water ; Cuwming,—Panama, do. common; C. B. Ad- 
ams.—Vancouver’s Straits, Mus. Cuming. 
Form squama. Tablet 1397 contains 8 sp. very young, of 
different sizes.—1398, 17 sp. different ages, striped.—1399, 5 
sp. different ages, colour not conspicuous. 
Form nivea, normal. ‘Tablet 1400 contains 6 sp. finely 
grown, with brown rays outside.—1401, 6 sp. do. without 
brown rays.—1402, 7 sp. with broad laminated margin ; one 
sp. measuring 1°7 outside, and 1°38 within ; another, measuring 
°97 within, has an apical margin *32 across.—1403, 4 sp. rough, 
laminated outside. 
Form striolata. Tablet 1404 contains 4 sp. beginning as 
squama, developing a few slight ridges.—1405, 5 sp. form nivea, 
irregularly developing ridges.—1406, 6 sp. ridges more deve- 
loped ; one being convex and closely ridged from the begin- 
ning.—1407, 2 sp. Lessonii-form developed, laminze close. — 
1408, 3 do. very irregular. (The two larger sp. are from a 
dealer, locality unknown, but among other Mazatlan shells.)— 
