MAZATLAN BIVALVES 



in other places I do not know, except from the picked speci- 

 mens in Mr. Cuming's Col. He regards the species as distinct. 

 The Mazatlan shells would never have encouraged any one to 

 unite them : neither Collector nor dealers offered to put them 

 together. I have very narrowly examined about 400 specimens 

 of this shell, and more than 600 of Ch. gnidia, nor did I find a 

 single intermediate form. The texture of the shells varies 

 as earthenware from china ; Ch. amathusia under the epidermis 

 being glossy, and of a very light brownish purple ; Ch. gnidia in 

 the same circumstances having the appearance of a baked shell, 

 dull, and of a darker brown. The concentric ribs are peculiarly 

 lustrous, and are very short and stumpy, rarely shewing any 

 tendency to rise into scales. The radiating stria? are very 

 much fainter, shewing a disposition to gather in twos in the 

 young shell. The lunular portion is much larger, smoother, 

 and of a richer purple. Both species within shew the middle 

 teeth slightly furcate, the paliial line distant from the margin, 

 and the sinus small. Ch. amathusia is generally smaller, more 

 swollen, with a thicker shell and margin ; and is more angula- 

 ted posteriorly. It is represented by Ch. cancellata in the 

 Caribbean sea, and its young may be the shell so named in 

 Menke's Mazatlan list. The smallest specimen found is 1*5 

 in. long ; the largest measures long. 2*43, lot. 2 '74, alt. 1'63. 



JTab. ? Panama, very rare, C. IB. Adams. S. W. Mexico, 

 P. P. C. Mazatlan ; Lieut. Green, (Gould ms.) Do. ; com- 

 mon and very fine ; L'pool fy Havre Coll. 



Tablet 341 contains 3 specimens, rounded form. 342, 3 do. 

 more angulated. 343, 3 do. close ribs. 344, 3 do. produced 

 posteriorly. 345, 3 do. distant ribs. 346, 3 do. swollen form. 

 347, 3 do. produced. 348, 3 do. even growth. 349, 1 do. witli 

 irregular ribs. In all 25 specimens. 



103. VENUS (? CHIONE) , sp. ind. 



This can scarcely be the young of Ch. amathusia, since the 

 shape is very different, being subquadrate. Surface more or 

 less distinctly marked with fine concentric ridges and radiating 

 striae, sometimes nearly smooth ; luuule clearly marked ; an- 

 terior tooth rather long; paliial line distant from margin; 

 sinus broad, shallow. Colour pink or light green. The largest 

 specimen measures long. '09, lot. '12, alt. '06. 

 Oct. 1855. h 



