MAZATLAN BIVALVES 113 



the following species, only a few valves have been found. They 

 are however described provisionally, as so little is known of 

 the tribe. 



161. MONTACUTA ELLIPTICA, n. S. 



JkT. t. obovali, planiuscwld, albd, marginibus undigue sa tis 

 excurvatis ; concentrice tenuissime striatd ; umbonibus promin- 

 entibus ; valvd alterd, fossa ligamentum recipiente, dent. card, 

 nullo, later alibus longis, gracilibus, ad marginem adJiarentibus ; 

 valvd alterd .....? 



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 

 insequilateral, but this is probably due to its youth, being only 

 "03 across. Long. *1, lat. '13, alt. *04 



Hab. Mazatlan ; off Chama and Spondylus, extremely rare ; 

 Lpool Col. 

 Tablet 502 contains the pair and largest valve. ' 



162. ? MONTACUTA SUBQUADRATA, n. s. 



I 



M. t. oblong d, subquadratd, solidiore, flavescente seu cinered ; 

 sulcis concentricis, creberrimis, rotundatis ; umbonibus appressis, 

 lunuld excavatd ; valvd Alterd dent. card, uno, inter fossas 

 duas, dent. lat. longis, prominentibus ; valvd alterd dent. card, 

 uno, elongato, prope marginem, fossa und, latd ; dent. lat. sub" 

 obsoletis. 



One perfect and two broken valves were found, which are 

 probably conspecific. The genus is doubtful: the hinge in 

 one valve resembles G-ouldia, and the shell 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 are on a raised plate, as in 

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

 oval Oolitic Astartidse. Long. '1, lat. '13, alt. '03. 



Hab. Mazatlan ; off Chamse, extremely rare ; L'pool Col. 



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

 ment that is supposed the opposite. 



