MAZATLAN BIVALVES 49 



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, lat. 1*52, alt. '5. 

 A subtrigonal one '92, 1'5^ ,, '52. 



The smallest '06, '0$ '02. 



2Iab.(D. culter) Mazatlan and Acapulco, Col. Chiming. Maz- 

 atlan ; common (the adult state rare, perhaps from burrowing 

 deeper in the sand) ; L'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, Desk, not Conr. Tablet 174 contains 10 sp. 

 with purple tinge predominant. 175, 9 jun. and 2 adult, very 

 transverse, 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, 9 sp. 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 insequivalve with sinuous margin.) 

 195, 12 sp. subtrigonal. 



Bayed 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. / 



