MAZATLAN BIVALVES AS) 
the shell: colour generally deep purple, with more or less of 
white. Epidermis very thin, deciduous. Umbos purple with 
white spot, occasionally rich orange. 
A transverse specimen measures long. °83, Jat. 1°52, alt. °5. 
A subtrigonal one 2 gE BOS, Ae), sale Doses oy ck yee 
The smallest i 5 #, MEE QOGR oeo5hiai4s OS.) sslannses 
fTab.—(D. culter) Mazatlan and Acapulco, Col. Cuming.—Maz- 
atlan ; common (the adult state rare, perhaps from burrowing 
deeper in the sand) ; LZ’ pool Col. 
Tablets 169—173 contain forms intermediate between this 
species and D. punctatostriatus.—169, 4sp. rayed.—170,°4 sp. 
purplish yellow.—171, 5 sp. purplish white.—172, 7 sp. yellow- 
ish.—173, 10 sp. more transverse. 
In the following series (except in the subtrigonal forms) the 
very young are D. culter, Hani., and the intermediate ones 
are generally D. contusus, Rve.: the white ones of both forms 
are D. Californicus, Desh. not Conr.—Tablet 174 contains 10 sp. 
with purple tinge predominant.—175, 9 jun. and 2 adult, very 
ransverse, margin sinuous, purplish gray.—176, 9 sp. less 
transverse.—177, regular form, 1 pair, 2 valves very young.— 
178, 11 sp. very oval and regular.—179, 12 sp. less transverse, 
more gibbous.—180, 12 sp. very gibbous.—181, 9 sp. subtrigonal. 
Yellowish var: 182, 9sp. transverse.—183, 7 sp. oval, gib- 
bous.—184, 6 sp. subtrigonal. 
Greenish var: 185, 11 sp. transverse.—186, 10 sp. gibbous.— 
187, 10 sp. subtrigonal. 
Greenish white : 188, 12 sp. very transverse.—189, 6 sp. sub- 
oval.—190, 7 sp. subtrigonal. 
Purplish white: 191, 12 sp. transverse.—192, 7 sp. subtri- 
gonal. 
White var: 193, 12 sp. very tranverse,—194, 12 sp. suboval 
(that marked* is curiously inequivalve with sinuous margin.)— 
195, 12 sp. subtrigonal. 
Rayed var: 196, 12.sp. very transverse.—197, 18 sp. oval.— 
198, 12 sp. subtrigonal. 
Tablet 199 contains 5 young shells (culter,) with the umbonal 
spot much developed.—200, 3 sp. (form contusus) yellowish 
white.—201, 3 sp. yellowish purple white. 
In all 292 specimens, no two being exactly alike. 
: Sept. 1855. ft 
