22 MAZATLAN BIVALVES 
S. Elena, D’Orbigny.—Panama, common, C. B. Adams.— 
Mazatlan ; extremely rare; L’pool Col. 
Tablet 75 contains 1 specimen, laid open. 
31. CORBULA BIRADIATA, Sow. 
Proc. Zool. Soc. 1833, p. 35.— Mull. Syn. Test. Viv. p. 230.— 
Fve. Conch. Ic. pl. 1, f.3.—Hanl. Suppl. Wood's Ind. Test. 
pl. 10. f. 51—Hanl: Deser. Cat.-p. 47.—B. M. Cat. D’ Orb. 
Moll. p. 70. no. 620. 
Shell with valves nearly equal, ventral margin flattened, 
posteriorly rather widely overlapping. Epidermis scarcely 
visible except at the margin, where it is, as usual, thick. Within, 
purplish white, ligament attached to larger tooth. Posterior 
muscular scar strongly marked, partly projecting, partly indent- 
ed, subcircular, with the little one behind coalescent. Anterior 
scar pear-shaped. Pallial line irregular; sinus very small. 
Long. °33, lat.°52, alt. °26. 
Hab.—Mud and sand, 3-6 fms., Chiriqui: 7 fm., in Bay of Came 
cas: Cuming. — Ecuador; Chiriqui: D Orbigny.—W .Columbia, 
Jay.—Panama, very rare, C. B. Adams.—Gulf of California, 
Mus. Cuming.—Mazatlan ; extremely rare: ZL’pool Col. 
Tablet 76 contains the only specimen found, in extremely 
fine condition, flattened. 
32. CORBULA PUSTULOSA, 2. 5. 
C. t. parva, alba, obesd, solidd, postice producta, truncata, 
antice rotundatd, ab umbonibus postice subangulata ; valva 
minore plus minusve tnclausd, maxime in margine ventrali ad 
posticwn decurrente, arcuata: valvis concentrice liratis, liris 
irregularibus, subrotundatis : epidermide tenwi, ad marginem 
erassd:: Lineis exillimis radiantibus pustularum 
minimarum repletis: umbonibus levigatis. 
Shell small, white, subglobose, produced posteriorly, with 
the valves overlapping, bent at the posterior end of the ventral 
margin; with irregular, somewhat rounded concentric ridges, 
crossed by the finest radiating lines, which under the microscope 
are found to consist of rows of minute pustules, probably 
formed in the epidermis, which is extremely thin over the body 
of the shell, coarse round the margin, and at the posterior side, 
which is rather angulated. 
Mr. Cuming’s specimen measures Jong. °16, lat. °24, alt. °14, 
The Mazatlan specimen a ed eh ees “11. 
