172 MAZATLAN UNIVALVES 
Cal. Shells, p. 5, Sta Barbara, Jewett,) which resembles T. 
infrequens much more closely than this species. All the three 
forms begin life as a small discoidal body, like a tumid Planor- 
bis. After making about two turns of this, they proceed in the 
regular way, affixing the disk vertically, or sometimes in a 
slanting direction, at the top of the spire. The length of spire in 
this species, which is not so rare as T. infrequens, is extremely 
variable. The smallest specimen is ‘037 long. The largest 
measures long. 11, long. spir. ‘02, lat. °05. The diseoidal apex 
is ‘005 across. 
Hab. — Mazatlan; on Chama and Spondylus, very rare ; 
*pook Col. 
Tablet 784 contains 5 sp. varying in age and shape, anda 
fragment to shew the apex. 
Famity BULLID. 
Genus BULLA, Klein. 
224. Butta Apamsti, Mke. 
Zeit. f. Mal. 1850, p. 162, no. 1. (syn. excl.) 
Dr. Menke regards this shell as that figured in Sow. Thes. 
Conch. f. 64,65, under the name of B. australis. In this he is 
probably mistaken, but not in regarding the species as distinct 
both from that and from B. Panamensis, Phil. It greatly 
resembles B. media, Phil. and still more B. major, Phil., both 
from the West Indies. It differs from the Upper Californian 
B. nebulosa, when adult, in being much smaller, more solid 
and contracted, and in having a much larger umbilicus. Shell 
chocolate coloured, very variously dotted with white, shadowed 
offin dark. Lip at the base strongly reflected, in the young 
shell distinct from the labium, which is well marked, white. 
Apex deeply umbilicate, shewing the whirls and with the inside 
spirally striated. The whole surface (described by Menke as 
smooth) is covered with extremely fine spiral microscopic strie, 
irregular, sometimes broken into dots by the striz of growth. 
Epidermis horny, thin. . Long. 1°38, lat. °91. 
Hab.—Mazatlan, Menke.—Do.: not common; L’pool Col. 
Tablet 785 contains 3 specimens approaching B. nebulosa 
in texture.—786, 2 do. normal form.—787, 2 do. more tumid, 
strong. 
