LUCINID^. 213 



with two diverging cardinal teeth in each valve, tlie anterior 

 being somewhat elongated and nearlj^ horizontally extended. 

 The absence of lateral teeth and the usual rounded and globose 

 form readily distinguishes this group from Corbis. The group 

 has been mistaken for Sphajra, under which name also most of 

 the species appear to have been described. Triassic, Creta- 

 ceous. G. llellivgi, Hauer (cxix, 54, 55). 



TJnicardium, d'Orbigny, 1852. 



Syn. — Mactromya, Agass. (part). 



Diafr. — Jurassic and Cretaceous. U. impressum, Morris and 

 Lycett (cxix, 58). 



Shell transversely oval, smooth or concentricallj^ striate ; 

 hinge with a single cardinal tooth in each valve, and no lateral 

 teeth. 



GONODON, Schafhaeutl, 1863. Shell ovate, tumid, apparently 

 smooth ; hinge of the right valve with a very large median semi- 

 circular broad tooth with the sharpened edge turned upwards, 

 that of the left valve with an equally large corresponding pit 

 below bounded by a long thick tooth somewhat smaller than 

 that of the other valve ; the posterior margins of the hinge are 

 thickened in both valves. This group differs from Unicardium 

 by the enormous development (natural ? ) of the teeth. Type, 

 U. ovatum, Goldfuss. Lias. 



CoNCHOCELE, Grabb, 1866. 



Type, C. disjuncta^ Gabb. Tertiary ; California. 



Shell subquadrate, posteriori}^ less high and elongated, being- 

 very inequilateral, a ridge passing from the beaks to the pos- 

 terior end; hinge edentulous, hinge-area somewhat thickened and 

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

 extending from the beak to the posterior end. As to internal 

 characters this genus hardly appears to differ fi'om some forms 

 of Unicardium in which the cardinal tooth is obsolete, but the 

 shape of the shell is different. 



FiMBRiELLA, Stoliczka, 1870. 



Type, F. laevigata, Sowh. (cxix ^ 5d). Cretaceous; England. 



Shell suborbicular, moderately tumid, subequilateral, with 

 prominent, obtuse, incurved beaks, surface partially smooth, 

 partially finely punctate or spinulous ; lunular edge in front of the 

 beaks somewhat expanded, hinge in each valve with two conical 

 or subtubercular cardinal teeth : those of the right are superim- 

 posed, 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 



