MAZATLAN UNIVALVES 231 



that of U. olivacea in being sharper at the outer edge, more or 

 less granular on the ridges (in the young shell over the whole 

 surface), and with the small interior rib beginning within the 

 other. Its apex fits against the periphery of the shell. A very 

 finely grown spreading specimen measures long. 1*2, lat. 1*7, 

 (without the palmae 1'36,) div. 80. The largest, conical sp. 

 measures long. 1*73, lat. 1'8, (without the palmse 1'56,) div. 60. 

 Hob. Mazatlan ; extremely abundant ; L'pool Col.S. W. 



Mexico, very fine, P. P. C. 



Tablet 1097 contains 5 sp. different ages, spreading variety. 

 1098, 6 sp. do. ordinary form. 1099, 3 do. conical. 1100, 3 do. 

 sculpture clear. 1101, 1 do. curiously mended after fracture. 

 1102, 1 do. upper part eaten away, leaving the liver chamber 

 with the whirls disunited, like Vermetus. 1103, 1 do. curiously 

 crowned with Coralline. 1104, 1 do. covered with Algae. 

 1105, 2 do. bored by young Lithophagi. 1106, 1 do. with large 

 Annelid, of which an operculum is added from a full grown 

 sp. on Spondylus, distinguished by the two large and two 

 small branching stag's-horn processes. 



Specimens skewing base. Tablet 1107 contains 3 sp., palmse 

 broad, expanded. 1108, 1 do. more distant. 1109, 1 do. very 

 narrow. 1110, 2 do. palmae numerous. 1111, 3 do. irregularly 

 developed. 1112, 1 do. with labium narrowed by Sabellariae, 

 which, along with Bryozoa contending with Vermetidse for 

 superiority, have covered the base. 1113, 1 do. with base 

 curiously rounded. 1114, 1 do. mouth blistered. 1115, 1 do. 

 with attachment of Calyptrseid outside the basal edge of the 

 mouth. 



Tablet 1116 contains 2 sp. with the opercula in situ, one 

 young, the other adult. 1117, 6 opercula. 



GENUS TROCHUS, Linn. 



Trochus, Linn., auct., pars iPhil. Hand. Conch, p. 210. The 

 ancient name is retained for these, the ordinary forms of the 

 original genus. 



Ziziphinus, Leach :H. & A. Ad. Gen. vol. i. p. 421 : Mon. 

 in Proc. Zool. Soc. 1851, p, 163. 



_- 289. TBOCHUS VEKSICOLOB, Mke. 



Zeit. f. Mai. 1850, p. 172, no. 32. 



P=Ziziphinus Californicus, A. Ad. Proc. Zool. Soc. 1851, p. 168, 

 no. 52. 



