MAZATLAN UNIVALVES 283 



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 strise 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, lot. 1*35, alt. '46. 

 Aflatsp. 1-46, 1'02, '14. 



A rounded, convex sp. '77, '68, 



An elongated sp. 1*35, '6, ,, 



Sp. a. Deck margin from vertex '77, from opposite end 

 Sp. b. '53, '8. 



Hab. Mazatlan ; abundant ; ISpool 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 ; 

 C. B. Adams. (C. Lessonii) Isle of Muerte ; under stones 

 at low water ; Cuming, Panama, do. common ; C. J3. 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. 14)1, 6 sp. do. wfthout 

 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-forrQ. developed, laminae close. 

 1408, 3 do. very irregular. (The two larger sp. are from a 

 dealer, locality unknown, but among other Mazatlan shells.) 



