MAZATLAN BIVALVES 113 



tlie folio wing species, only a few valves have been found. They 

 are however describod provisionally, as so little is known of 

 the tribe. 



161. MOXTACTJTA ELLIPTICA, n.S. 



M. f. ohovali, planmscul'i, albd, margimbim undique sa tis 

 excurvatis ; concentrice tcnuissime striata; nmhonihns promin- 

 entihus ; valva altera, fossa Ugamentiim recipiente, dent. card, 

 nullo, lateralibiis lonr/is, graciUbus, ad margineni adlimrentihus ; 

 valrd altera ... .? 



Only 2 valves (not opposite^) and one minute pair which I 

 have not dared to open, were found of this species. The shape 

 is very regular, and the teeth very slender. The pair is less 

 ingequdateral, but this is ijrobably due to its youth, being only 

 '03 across. Long. '1, lat. '13, alt. 'Ol. 



Sab. — Mazatlau ; off Chama and Spondjdus, extremely rare ; 

 L'jjool Col. 



Tablet 502 contains the pair and largest valve. 



162. ? MONTACUTA SUBQUADEATA, n. S. 



M. t. oblongd, subquadratu, solidiore, flavescente seu cinerea ; 

 siclcis conce7itricis, creberrimis, rotundatis ; timbonibus appressis, 

 lunula excavatd ; valvd altera dent. card, tino, inter fossas 

 duas, dent. lat. longis, promincntihus ; valvd alter d dent. card, 

 una, elongate, prope margineni, J'ossd und, lata ; dent. lat. sub- 

 obsoletis. 



One iierfect and two broken valves frerc found, which are 

 probably conspecilic. Tlie genus is doid^tful : the hinge in 

 one valve resembles Gouldia, and the shcU is too much worn 

 to determine the position of the ligament. It appears as 

 though there were two cardinal teeth interlocking, with the 

 ligament occupying the second pit : but instead of the hinge 

 area being interrupted, the pits arc on a raised plate, as in 

 Mactra, &c. Outside it resembles in miniature some of the 

 oval Oolitic Astartidsc. Long. '1, lat. '13, alt. "03. 



Sah. — Mazatlan ; off Chama), extremely rare ; L'pool Col. 



Tablet 503 contains the large perfect valve, with the frag- 

 ment that is supposed the opposite. 



