114 MAZATLAN BIVALVES 
162. Montacuta ————, sp. ind. 
Tablet 504 contains a fragment of a stout shell, in many 
respects like ? M. subquadrata ; but entirely destitute of car- 
dinal teeth. The lunule is much incurved: indistinct ridges 
run from the prominent umbo to the anterior and posterior 
margins ; surface concentrically striated ; hinge margin inter- 
rupted, with large sunken cartilage pit bounded by 2 marginal 
callosities, but no lateral teeth. The shell when perfect was 
probably larger than the last. 
Hab.—Mazatlan ; off Chama; L’pool Col. 
Famity CYCLADID A. 
Genus CYRENA, Lam. 
164. CYRENA OLIVACEA, 7. s. 
C. t. compressa, subtrigond, levi, vel striis incre- 
mentt haud impressis, epidermide olivacea indutéi; margine 
ventrali excurvato, posticum versus plerumque sinuato ; postico 
angulato, subrostrato ; latere dorsali antico declivo, vix alato ; 
wmbonibus satis prominentibus, ligamento elongato ; epidermide 
wmbones tegente, lamellis parvis corrugatis pler- 
wmgque indutd, maxime angulam posticam versus ; intus pur - 
pured, maxime umbones et marginem versus ; dent. card. il., 
quarum alter valva antiet duo, alterd postict duo, bifidi sunt ; 
lat. 2-2, 1-1, parvis, levibus, extantibus, quarum antict pro- 
pingut, postict remoti sunt; sinu pallii parvo, triangulari, 
angustissimo. 
=(C. Fontainei, Desh. ms. in B. M. et Mus Cuming, et P. P. C. 
in Cat. Prov.: non D’Orb., ad fid. spec. typ.: nec Phil. in 
Zeit. f. Mal. 1851, p. 70, no. 93. 
This shell has been freely distributed as C. Fontainei, 
DOrb., on the authority of M. Deshayes, who having the 
original types to consult, was supposed to be correct. The 
true C. Fontainei, however, is amore regularly formed shell, 
with faint concentric ribs and a glossy epidermis, and appears 
identical with C. placens, Hanl. 1844. The species which Philip- 
pi has described under the same name is distinct from either : 
it may prove to be the following. C. olivacea is known out- 
wardly by its flattened form, generally beaked posteriorly ; 
