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. MontTacUTA ELLIPTICA, 2. s. 
M. t. obovali, planiusculd, albd, marginibus undique sa tis 
excurvatis ; concentrice tenuissime striata ; umbonibus promin- 
entibus ; valvd alterd, fossa ligamentum recipiente, dent. card. 
nullo, lateralibus longis, gracilibus, ad marginem adherentibus ; 
valvé 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 
inequilateral, 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 ; 
P’pool Col. 
Tablet 502 contains the pair and largest valve. 
162. ? MonTacuTA SUBQUADRATA, 2. S. 
M. t. oblonga, subquadraté, solidiore, fiavescente seu cinerea ; 
suleis concentricis, ereberrimis, rotundatis ; umbonibus appressis, 
lunula excavaté; valvd altera& dent. card. uno, inter fossas 
duas, dent. lat. longis, prominentibus ; valvd alterd dent. card. 
uno, elongato, prope marginem, fossa und, laté ; 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 Gouldia, 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, &e. Outside it resembles in miniature some of the 
oval Oolitic Astartide. ong. °1, lat. ‘13, alé. °03. 
Hab.—Mazatlan ; off Chame, extremely rare; L’pool Col. 
Tablet 503 contains the large perfect valve, with the frag- 
ment that is supposed the opposite. 
