116 3IAZATLAN BIVALVES 



that it is the same shell. In order, hovrever, to include the 

 whole of the si^ecies, 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" 

 hy. 3IaJ. H/'ck ; another "?'Msiza.t\an" hj 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. Corh. it has probably been merged 

 into another, perhaps C. Floridaua. 



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 bi'ownish olive, with the lajers 

 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 naiTOw 

 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 anythingbut attractive, the mside is often 

 extremely rich and beautiful. The young shells (of which an 

 abundance were s3nt, 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. 



A young transverse sp. ,, 1'13, ,, 



The largest sp. ,, 2' 15, ,, 



Mr, Darbishii'c's sp. „ 1'67, ,, 



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. — 520, 5 do. subtrigonal. — 521. 4 do. posterior 

 part subangulated. — 522, 6 specimens shewing the interior. 



