134 mazatlaif bivalves 



181. Aeca multicostata, Sow. 



Proc. Zool. Soc. 1833, p. 21.— i?ir. Conc/i. Ic. pi. 4, f. 23.— 

 Sanl. Rec. Shells, pi. 19, f. 12. 



One very fine specimen of this shell was found by IVIr. Archer. 

 It differs from A. grandis in being much lighter, with more 

 numei-ous ribs, and a squarer form. Xo»g. 2"65, lat.Z'lQ, 

 alt. 2-36. 



Hab. — Gulf of Tehuantepec, 12 fm., Ci/M/wfir- ^lazatlan; ex- 

 tremely rare ; L'pool Col. 



Tablet 628 contains a very small valve, '1.5 across, which 

 raaj- belong to this species.— 629, a drawing of Mr. Archer's 

 specimen. 



182. Aeca Plabiata, Smo. 



Proc. Zool. Soc. 1833, p. 21.—Rve. Conch. Ic. pi. 1, f. 7.— 



Hani. Descr. Cat. p. 160.— J5. M. Cat. B'Orb. Moll. p. 81, 



no. 720. 

 Comp. A. labiosa, Soic. loc. cit. — Sve. Conch. Ic. pi. 10, f. 67. — 



JIanl. Descr. Cat. p. 1.59, pi. 19, f. S.—P. 21. Cat. B'Orb. 



Moll. p. 81, no. 720. 

 Comp. A. incongrua, Say, Journ. Ac. Nat. Sc. Phil. vol. ii. 



p. 2m.— Saul. Descr. Cat. p. 159. 



The three species above quoted are very nearly allied. The 

 two specimens found in the L'pool Col. by Messrs. Hibbert 

 and Archer, bcfoi'c it fell into the dealer's hands, are exactly 

 like the specimens brought from Florida, by J. J. Audubon. 

 Shell with distant bealvs, and strong ligament fdling up a large 

 rhomboidal area. Shape subangular; tubercles absent from 

 the angular part, also from the front of the smaller valve. 

 Teeth rather broad. Long, (fromximbo) 1"23, lat. \'Z, alt. 1"04. 



Hub. — ^Real Llejos and Turabez, Peru, in sandy mud, 7 ftn, 

 Cuinlnf/. — ]Mazatlan ; extremely rare ; Upool Col. 



Tablet 630 contains a specimen, presented by J. Hibbert, Esq. 



183. Akca bifeoks, n. s. 



A. t. turgidd, subquaJratd, tenui, majcime incpqnivalvi, postice 

 angulatd, umbonihus haud distantibus ; albd, epidcrmide Icevi , 

 olivaced indutd ; costis circiter xxx., in testa juniore omnibus 

 tuberculosis ; in adultd solum viii. — x. anticis, rcliquis lavibus ,- 

 costis ventralibus in v ale d m in ore p a r v is , rotundatis. 



