MAZATLAN BIVALVES 95 



satis ; parte anteriore punctis ovalihus impressis decussatd ; 

 dentibus lateralibus approximatis. 



Tliis cliarmiug little creature lias a general resemblance to a 

 minute C. costatiim ; but tbe large ventral costse are ratber 

 rounded, witb a little one on eacb. side making tbem appear 

 somewbat trigonal. Tbe anterior portion is strongly indented 

 witb oval pits. Tbe appearances it presents under tbe micros- 

 cope vary greatly according to tbe direction of tbe ligbt. Tbe 

 young sbells bave fewer ribs near tbe binge, wbere tbe teetb 

 are not fully developed ; are ratber less sequilateral ; and are 

 granulose on tbe ribs. Long. '12, lat. '11, alt. "08. 



Hah. — Mazatlan ; in Cbama and Spondylus wasbings ; ex- 

 tremely rare. 



Tablet 461 contams 2 valves, tbe largest and tbe smallest. 



134. Caedium g-eanifebum, Brod. Sf Soto. 



Zool. Journ. vol. iv. p. Z&J.—Soio. Conch. III. no. 38, pi. 49, 

 f. 17.—Rve. Conch. Syst. pi. 76, f. 17 -.—Conch. Ic. pi. 8, 43.— 

 Hani. Descr. Cat. p. 137.-0. B. Ad. Pan. Shells, p. 266, 

 no. 430.— 5. M. Cat. D'Orh. Moll. p. 73, no. 652. 



Tbe smallest valve found, wbieb only measures '03 across, 

 scarcely sbews a trace of teetb. Tbe young sbells are nearly 

 rectangular at tbe posterior end ; wben older, tbey are obtuse 

 angled. Tbe interstices between tbe ribs are decussated by a 

 series of rectangular impressed pits laid transversely. Tbe 

 largest specimen found measures only long. '12, lat. -12, alt. 'OB. 

 Hab.—T>\\g from a deptb of about 6 incbes in tbe mud of tbe 

 Estaro de Mazatlan ; Lieut. Belcher.— GaA? of Nicoyia and 

 Xipixapi; Cuming, TfOrhigny. — Panama, extremely rare, 

 C. B. Adams. — Mazatlan ; a very few young valves and frag- 

 ments in tbe wasbings of Cbamaj and Spondyli ; L'pool Col. 



Tablet 462 contains tbe largest (imperfect) valve, and two 

 small ones. 



135. PCaedium , sp. ind. (g.) 



? C.t. juniore .mhorhiciilari, alhidd, valde incequilateraU ; 

 margine dorsali postice redo, antice concavo ; costis circiter xviii, 

 validis, rotundatis, approximatis, tuherculis latis armatis ; 

 dentibus elongatis, lateralibtis distantibus. 



