227 

 Trigonia — continued. 



crenulata. . ovato -trigonal, produced forwards, many ribbed ; 

 ribs transverse, bowed, obliquely crenated, with numerous 

 oblong crenulations. . Mons. 



aspera. . ovato-trigonal, subcompressed, produced forwards ; 

 ribs transverse, remote, tuberculatedly rough ; corselet 

 raised, more smooth, but carinated. . 



dcedalea. . ovato -rhomboidal, subangulated, rather depressed, 

 fore part with rather large hemispherical tubercles in 

 transverse rows ; hinder, with smaller tubercles in varying 

 directions. . Coulaines. 



navis. . ovato-trigonal ; extended and compressed forwards ; 

 longitudinal tuberculato-nodose ribs ; hinder area flat, 

 transversely ribbed. 



costata. . ovato -angulated ; trigonal ; ribs smooth, transverse ; 

 corselet large, longitudinally grooved, carinated in the 

 upper part. . Havre. 



sulcataria. . trigonal-subcuneated, produced anteriorly, and 

 becoming thinner ; posterior transverse and anterior lon- 

 gitudinal grooves ; corselet striated transversely. 

 • ' sinuosa. . ovato- angulated, trigonal ; transverse smooth ribs, 

 sinuously angular ; corselet smooth. 



rugosa. . ovato-trigonal, depressed, subangulated, with trans- 

 verse rugeeform ribs ; anterior ones smooth, posterior 

 subtuberculated. 



crassatellina. . trigonal, depressed, with transverse angularly 

 plaited grooves ; margin crenulated. 



cardissoides. . cordated ; depressed on the sides, valves raised in 

 a flat keel on the back ; beaks prominent, rather remote. 

 Assumed to be of this genus, but the hinge not known. 



injlata. . trigonal, turgid, produced forwards, wedge-shaped, 

 rather smooth, truncated behind ; the posterior area much 

 cordated. 

 Bourguet, Petrif. 153. 



arcuata. . trigonal ; longitudinal ; bowed ribs ; obsolete, decus- 

 sating transverse grooves ; beaks compressed. 



Chama. 



IcBvigata. . left-turned, smooth, fixed obliquely ; small valve flat, 



subconcave. 

 gryphina. . left-turned, imbricated ; with unequal, for the most 



part, depressed squamse on the smaller valve ; the border 



partly crenulated. . Piedmont. 

 lacernafa. . the smaller valve flat, subantiquated ; thick waving 



transverse frills, back longitudinally striated . . Mont 



Marius. 

 turgidula.. rounded, turgid; small valve convex, imbricated, 



with short overlying lamellae ; back striated. 

 echinulata. . oval, tumid, echinated with numerous subtubulated 



squamulse. . Plaisance. 



