ORDER III 



TELEODESMACEA 



397 



more specialised modern representatives there is no appreciable ligament remaining, and the 

 ivsiliuin has become large and deeply immersed. The parallelism between 

 this ^roup and the Madridac, in the gradual immersion of the ligament, 

 could hardly be more complete. 



Orassatelliies, Kruger (Crassatella, Lain., 1819, non Lam., 1799), 

 (Figs. 710, 711). Cretaceous to Recent ; represented by about seventy 

 fossil and forty living species. 



Triodonta, Koenen. Oligocene. Scambula, Conrad : 1!> unnuHn, ( !;il.li 

 (Stearnsia, White) ; Anthonyia, Gabb ; Crassatellina, Meek. Cretaceous. 



? Ptychomya, Ag. Like Crassatellites, but with radial sculpture 

 and three cardinals in each valve. Cretaceous. 



Crassinella, Guppy non Bayle (Gonllia, auct. non Adams ; 

 Pseuderiphyki, Fisch.) Small, sub-triantrular, very compressed, con- 

 centrically ribbed. Tertiary and Recent. 





Oligocene; Wein- 

 1 "' ne 



Superfamily 3. CYRENACEA. Tryon. 



Cypricardians which have become specialised for fresh or brackish water conditions, 

 and, as usual in such cases, have developed great variability of character. 



Family 6. Oyrenidae. Gray. 



Shell porcellanous, with a conspicuous epidermis, usually with concentric sculpture ; 

 valves equal, free, closed, usually with plain margins; area obscure or none; ligament 

 and resilium external, parivincular, opisthodetic ; adductor scars sub-equal, separate 

 from the pedal ; pallial line simple or with a small sinus ; hinge with anterior and 

 posterior laterals usually double in the right, single in the left valve, distinctly separated 

 from the cardinals; cardinal teeth bifid at the summit, three in each valve when none 

 are obsolete. Mantle open ventrally, the siphons distinctly developed, short, more or less 

 united. Lias to Recent. 



Many of these forms merge with one another as we recede in time. The recent American 

 forms and many fossils show a pallial sinus ; oriental species are generally without it. In 

 some fossils the laterals of the right valve are not double. 



Cyrena, Lam. Rounded, nib-equilateral, plump, concentrically sculptured, with 

 smooth margins; cardinals three, the laterals smooth. Lias to Recent (300 spt !,- : 



maximum in tin- -Cre- 

 taceous and onwards. 



Sub-genera: Corbi<-uJ,i. 

 Megerle (Figs. 712, 713). 

 Smaller than Cyrena, and 

 the laterals sharply cross- 

 striated. Egeta, Adams. 

 Compressed, elongated, 

 thin ; almost rostrate. 

 Recent ; marine. 



FIG. 712. 



Corbicula fluminalis, 

 Mull. sp. Pleistocene ; 

 Teutschenthal, near 

 Halle, Saxony. 



FH;. 713. 



Corbicula semistriata, Desh. Oligocene (Cyrena 

 marls) ; Flonheim, near Alzey. !/! 



Batissa, Gray. Like 

 Cyrena, but the right 

 anterior and left posterior cardinals feeble or obsolete ; anterior laterals very short, 

 posterior ones elongated. Upper Cretaceous of Oregon, and living in Indo-Pacific 

 region. 



Veloritina, Leptesthes, Meek. Laramie Group. Velorita, Gray. Recent. The 

 relations of the recent Galatea, Brug., and Fischeria, Bernard i, do not seem to be 

 positively fixed. 



