246 CEETACEOUS PELECYPODA 



more numcrovis than at the present time. If all the other eocene deposits be 

 as rich in lucjni^\e as those of the Paris hasiii, the suh-family T^oiild seem to 

 possess its greatest development during the time of that formation, for the total 

 number of recent species is somewhat short of that wiiich Dcshayes describes 

 from the Paris basin alone. In the present seas the distribution is universal, but 

 the species seem to be with few exceptions far from common. 



I will first give a review of the known genera, and then a list of those forms 

 which have been recorded from cretaceous deposits. The South Indian rocks have 

 yielded us examples of many of the generic types, and several very interesting 

 new species : — 



a. Siih-f.nnU^—COBBINy'E. 



1. Uiiicardhim, d'Orb., 1850, (Prod, de Paleont., i, p. 218). Shell elon- 

 gately oval, or ovally rounded, sub-inequilateral, of moderate thickness, beaks 

 tumescent, incurved and close together, surface concentrically striated, hinge with 

 one conical cardinal tooth in each valve, sometimes becoming obsolete or nearly 

 so, fulcra long and prominent, separated from the margin by a deep furrow in 

 which the ligament is lodged. Type, U. carcUoides, Phillips, sp. fCorhuIa id. J, from 

 the Lias. The species of Unicardium are as yet chiefly known from Jurassic beds ; 

 there are some triassic species described under the names of Lucina and Covhh, 

 which may belong to it, but their hinges have not yet been made known. In 

 cretaceous deposits the genus becomes apparently very rare. 



2. Conchocele, Gabb, 1866, (Pal. Calif., vol. ii, p. 27). Shell sub-quadrate, 

 posteriorly less high and elongated, being very inequilateral, a ridge passing from the 

 beaks to the posterior end, hinge edentulous, hinge area somewhat thick(>ned and 

 insinuated under the beak with a single long rib-like tooth extending from the 

 beak to the posterior end. Type, C. disjuncta, Gabb, from tertiary beds of Cali- 

 fornia. As to internal characters this genus hardly appears to differ from some 

 forms of Unicardium in which the cardinal tooth is obsolete, but the shape of the 

 shell is different. 



3. Fimhriella, Stol., 1870. Shell sub-orbicular, moderately tumid, sub- 

 equilateral, with prominent, obtuse incurved beaks, surface partially smooth, 

 partially finely punctated or spinulous; lunular edge in front of the beaks 

 somewhat expanded, as in the two following genera; hinge in each valve with 

 two conical or sub -tubercular cardinal teeth: those of the right are super- 

 imposed, the upper one being situated on the enlarged lunular margin, those of 

 the left valve are situated' beside each other, the anterior much stronger than 

 the posterior, no lateral teeth are present, but the margin is posteriorly internally 

 slightly grooved; the ligament must have been thin, for there is only a short 

 very narrow space immediately behind the beaks for its attachment, no special 

 nymphye being present. Type, Corhiila IcvvUjafa, Sow., (Min. Conch., iii, p. 16, 

 pi. 209, figs. 1-2), a cretaceous shell from the Blackdown sandstone ; it has been 

 transferred by d'Orbiguy to Vnic((rdiin», but diftcrs by the number and position of 



