372 MAZATLAN UNIVALVES 



and C. cervus of Linn. The species was adopted for geographi- 

 cal reasons by Prof. Adams, who regarded all the W. Indian 

 shells as C. exanthema, all those from the W. coast as C. cer- 

 vinetta, and all those from the Polynesian islands as C. cervus 

 ( = cervina). While however the S. W. Mexican shells belong 

 clearly and exclusively to the type C. cervinetta, those from 

 Mazatlan belong with almost equal exclusiveness to the typical 

 C. exanthema. An examination of several hundred specimens 

 shews that the characters usually relied on to separate the 

 species, are by no means constant. The Mazatlan shells rarely 

 develop inner dots ; but the number of spots is extremely 

 variable, one specimen exhibiting on the labral half the numer- 

 ous small spots of C. cervus, on the labial half the distant ocel- 

 lated spots of C. exanthema. The anterior dilation of the mouth 

 is also variable, generally taking the open form of C. cer- 

 vinetta, but sometimes the narrower shape of C. exanthema. 

 The columellar indentation and markings are also variable. 

 Sometimes the posterior labral deposit equals the labial, some- 

 times decidedly exceeds it, sometimes falls still more below it. 

 The size is very rarely small as in C. cervinetta ; generally 

 elongated as in C. exanthema, occasionally large and swollen 

 as in C. cervus. The colour is either light or dark ; with the 

 bands varying in distribution, and the mantle line generally 

 straight, sometimes waved. A swollen adolescent specimen 

 measures long. 3 '44, lot. 2*04. 



A cylindrical sp. 3*5, 1'66. 



Hab.'W. Indies, passim. Barbadoes, fossil, Dr. Cutting. 

 (C. cervinetta,) Panama and Taboga ; 115 sp. at and just 

 above low water mark of spring tides, under stones 15-20 in. 

 in diameter ; C. B. Adams. S. W. Mexico, common,* 

 P. P> C. Mazatlan ; not uncommon ; L'pool Col. 

 Tablet 1734 contains 3 sp. adolescent, banded. 1735, 1 do. 

 form cervus. 1736, 3 sp. spots beginning, 1737, 3 sp. adult, 

 bands evident. 1738, 3 do. bands concealed. 1739, 3 sp. adult, 

 light colour, spots very faint. 1740, 1 do. spots decided. 1741, 

 1 sp. slightly spotted, not banded, resembling C. talpa. 1742, 

 1 sp. right with few ocellated spots, left with close numerous 

 simple ones. 1743, 2 sp. with ocellated spots ; one small, type 



* Before I was aware of the separation of C. exanthema and cervinetta, I un- 

 fortunately mixed some small specimens of the latter from the S. W. Mexican 

 collection with those from Mazatlan, (the box from the latter having been 

 temporally mislaid,) and distributed them accordingly. Those of the true C. c 

 vinetta type were extremely rare in the Mazatlau collection. 



ae C. cer- 



