MAZATLAN BIVALVES 73 
in other places I do not know, except from the picked speei- 
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. Ihave 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 avery light brownish purple ; Ch. enidiain 
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 strie are very 
much fainter, shewing a disposition to gather in twos in the 
young shell. The lunular portion is much larger, smoother, 
and of aricher purple. Both species within shew the middie 
teeth slightly furcate, the pallial 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, lat. 2°74, alt. 1°65. 
Hab.—? Panama, very rare, C. B. Adams.—S. W. Mexico, 
P. P. C—Mazatlan; Lieut. Green, (Gould ms.)—Do. ; com- 
mon and very fine; L’pool & Havre Coll. 
Tablet 341-contains 3 specimens, rounded form.—342, 8 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. with 
irregular ribs. In all 25 specimens. 
103. Venus (? Co1onz) ————, 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 
striz, sometimes nearly smooth; lunule clearly marked; an- 
terior tooth rather long; pallial line distant from margin ; 
sinus broad, shallow. Colour pink or light green. The largest 
specimen measures long. ‘09, lat.°12, alt. *06. 
Oct. 1855. ‘ h 
