116 MAZATLAN BIVALVES 
that it is the same shell. In order, however, to include the 
whole of the species, a new description is appended, which 1 
had drawn out under the name, C. varians, which is certainly 
not inappropriate. A very extreme form, also found by Mr. 
Darbishire in the L’pool Col., has been named C. altilis by 
Dr. Gould, from specimens, one of which is marked ‘‘ Mexico” 
by Maj. Rich; another ‘‘? Mazatlan” by Col. Jewett. Some 
of the young shells are ticketed C. fragilis in the Cumingian 
Collection; but as the name does not appear either in the 
P. Z. S. nor in the Cat. Corb. it has probably been merged 
into another, perhaps C. Floridana. 
Although the general appearance of these shells is sufficiently 
distinct from C. olivacea, yet there are many points of resem- 
blance between individuals. This species however, is much more 
variable ; almost always more ventricose ; epidermis thinner, 
more deciduous, of a dirty brownish olive, with the layers 
very close and thin, not corrugated. These layers are gener- 
ally abraded, as are the umbos. The anterior cardinal teeth 
are rather more elongated: the lateral teeth rather more 
elevated ; the pallial sinus is rather triangular, not so narrow 
as it generally is in C. olivacea. The violet colour is also of a 
somewhat lilac tinge, and very rarely covers the whole shell. 
While the outside is anything but attractive, the inside is often 
extremely rich and beautiful. The young shells (of which an 
abundance were sent, but very few of C. olivacea, jun.) vary 
quite as much as the adults. Of the most aberrant, suborbi- 
cular form, Mr.-Darbishire possesses a fine swollen specimen, 
with the umbos not abraded, and greatly resembling (except 
in the epidermis and the inequality of the teeth,) the speci- 
men, tablet 511, of the last species. A young suborbicular 
specimen measures long: °95, lat. 1°06, alt. °76. 
A young transverse sp.,, 1°13, ,;, 1°5, rage ats 6 (e 
The largest sp. 39, CDs | Page seas iL igs) de AG: 
Mi Darbishires sp.) -,.! -L°G#s) 2 s4cck Fay 4, PALO: 
Hab.—Mazatlan ; not common; L’pool Col. 
Tablet 512 contains 4 specimens, very regular outline, sub- 
orbicular.—513, 4 do. slightly transverse.—514, 4 do. a little 
more transverse.—515, 5 do. very transverse.—516, 4 do., the 
same, slightly swollen ventrally.—517, 4 do. rather more 
swollen.—518, 5 do. less transverse, normal state.—519, 4 do. 
margin regular.—d520, 5 do. subtrigonal.—521, 4 do. posterior 
part subangulated.—522, 6 specimens shewing the interior. 
