MAZATLAN BIVALVES 49 



the shell : colour generally deep purple, vritli more or less of 

 white. Epidermis very thin, deciduous. Umbos purple with 

 white spot, occasionally rich orange. 



A transverse specimen measures. Softs'. '83, lat, l'o2, alt. '5. 

 A subtrigonal one „ ,, "92, ,, 1"53, ,, •52., 



The smallest „ „ „ '06, „ "OS, „ '02. 



Hah.—CD. culter) Mazatlan and Acapulco, Col. Cuming.— Maz- 

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

 deeper in the sand) ; U-pool Col. 



Tablets 169—173 contain forms intermediate between this 

 species and D. punctatostriatus. — 169, 4 sp. 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. coutusus, Svc. : the white ones of both forms 

 are I). Californicus, Desk, not Conr. — Tablet 174 contains 10 s]). 

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

 transverse, margin sinuous, puii^lish gray. — 176, 9 sp. less 

 transverse. — 177, regular form, 1 pair, 2 valves very young.— 

 178, 11 sp. very oval and regidar.— 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. 



G-reeuish 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. sul)trigonal. 



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. 



Rayed var : 196, 12 sp. very transverse. — 197, 18 sp. oval.— 

 19^, 12 sp. subtrigonal. 



Tablet 199 contains 5 young shells (culter,) with the umbonal 

 spot much developed. — ^2<^), 3 sp. (form contusus) yellowish 

 white. — 201, 3 sj). j-eUowish inirple white. 



In all 292 specimens, no two being exactly alike. 

 Sept. 1855. / 



