ORDER III TELEODESMACEA 397 
more specialised modern representatives there is no appreciable ligament remaining, and the 
resilium has become large and deeply immersed. The parallelism between 
this group and the Mactridae, in the gradual immersion of the ligament, 
could hardly be more complete. 
Crassatellites, Kruger (Crassatella, Lam., 1819, non Lam., 1799), 
Figs. 710, 711). Cretaceous to Recent ; represented by about seventy 
fo) ) ? e 
fossil and forty living species. 
Triodonta, Koenen. Oligocene. Scambula, Conrad ; Remondia, Gabb 
Stearnsia, White) ; Anthonyia, Gabb ; Crassatellina, Meek. Cretaceous. 
5) ’ 5) ’ ry 
? Ptychomya, Ag. Like Crassatellites, but with radial sculpture 
and three cardinals in each valve. Cretaceous. vie (0s 
ose pene |? 1 ; ees ve Fe . . oH Crassatellites 
Crassinella, Gupp) ae Bayle (Gouldia, auct. non Adams ; Bronni,  Merian. 
Pseuderiphyla, Fisch.) Small, sub-triangular, very compressed, con- Oligocene; Wein- 
3 : é heim, near Alzey. 
centrically ribbed. Tertiary and Recent. iO : 

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. Cyrenidae. 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, sub-equilateral, plump, concentrically sculptured, with 
smooth margins ; cardinals three, the laterals smooth. Lias to Recent (800 species) ; 
maximum in the Cre- 
taceous and onwards. 
Sub-genera: Corbicula, 
Megerle (Figs. 712, 713). 
Smaller than Cyrena, and 
the laterals sharply cross- 
striated. Hyeta, Adams. 
Compressed, elongated, 
thin; almost rostrate. 

Fig. 712. 
Corbicula fluminalis, ‘a. 7 R ; ‘j 
= Pb (iss ecent ; ma 2. 
Miill. sp. Pleistocene ; Higeents aire 
Teutschenthal, near Corbicula semistriata, Desh. Oligocene (Cyrena Ratise ate = 
Halle, Saxony. marls); Flonheim, near Alzey. 1/}. 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, Bernardi, do not seem to be 
positively fixed. 
