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, lot. '05. The discoidal apex 

 is '005 across. 



Sab. Mazatlan ; on Chama and Spondylus, very rare ; 

 Jj'pool Col. 



Tablet 784 contains 5 sp. varying in age and shape, and a 

 fragment to shew the apex. 



FAMILY BULLID^E. 

 GENUS BULLA, Klein. 



4" 224. BULLA ADAMSI, Mice. 



Zeit.f. Mai. 1850, p. 162, no. 1. (syn. excl.) 



Dr. Menke regards this shell as that figured in Sow. TJies. 

 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 Calif ornian 

 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 

 off in 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 striae, 

 irregular, sometimes broken into dots by the striae of growth. 

 Epidermis horny, thin. Long. 1*38, lat. '91. 

 Sab. 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. 



