ORDER III TELEODESMACEA 399 
Carditamera, Conr. Elongated, sub-mytiliform. Plewromeris, Conr. Small, 
equilateral, trigonal. Calyptogena, Dall.  Ovoid, smooth externally. Carditella, 
Smith. Small, with internal ligament. All Tertiary and Recent. Thecalia, Adams ; 
Milneria, Dall. Females with a shelly marsupium. Recent. 
Superfamily 5. CHAMACEA. Geinitz. 
Carditian forms specialised for a sessile habit, usually with exceptionally spiral 
growth, and very unequal valves. Marine. 
Family 9. Chamidae. Lamarck. 
Shell substance three-fold, the inner layers porcellanous and tubular, the middle 
obscurely prismatic, the external cellulo-crystalline with reticulated tubules and an incon- 
spicuous epidermis; valves wnequal, trreqular, one of them sessile ; closed, usually 
rounded in form with conspicuous sculpture, often differing in the opposite valves; ad- 
ductor scars sub-equal, elongate, pedal scars minute, distant ; ligament and resilium 
external in a deep groove, parivincular, opisthodetic ; area distinct, prosodetic ; beaks more 
or less spiral, prosogyrous; pallial line simple; hinge plate heavy, arcuate; hinge 
frequently with a minute or obsolete posterior lamina, chiefly in the fixed valve ; cardinals 
one or two in the free valve, two with an intermediate socket in the fied valve; the 
anterior cardinal broad, usually deeply grooved or multifid, the posterior simple, long and 
curved parallel with the dorsal border; siphonal orifices not produced into tubes; adductors 
each composed of two elements. Cretaceous to Recent. < 
Either of the valves of Chama may be the sessile one, but the teeth in the fixed valve, 
whether right or left, are always the same, and similarly with the free valve. The fixation 
is generally by the left valve. 
Chama, Lin. (Fig. 716). Nepionic shell rounded. Ligament sometimes continued 
to the point of the beaks, as 
in other bivalves with gyrate 
umbones; form rounded, 
attached valve deeper and 
larger, the free valve flatter ; 
margins usually cross- 
striated, surface lamellar or 
spinose ; adductor scars large, 
not elevated. Cretaceous to 
Recent; maximum iin 
Eocene. 
Echinochama, Fisch. Nepionic shell elongated, having the form, hinge, and other 
characters of Cardita ; attached when adolescent, free in the young and adult stages. 
Valves sub-equal and similar ; surface vermiculate, spinose, with radial ribs. Oligocene 
and Recent. 

Fic. 716. 
Chana squamosa, Lam. Eocene; Hampshire. 1/;. 
Family 10. Diceratidae. Dall.! 
Resembling Chama, but with the adductors usually borne on myophoric laminae, or 
projections which are prolonged into the umbonal cavity below the hinge plate; valves 
1 Por the Chamacea and Rudistae, Neumayr proposed the term Pachydonta. For special litera- 
ture see: Zittel, K. A. von, Die Bivalven der Gosaugebilde (Denkschr. Akad, Wissensch. Wien, Bd. 
XXIV.), 1864.—Gemimellaro, G'. G., Caprinellidae della Ciaca dei intorni di Palermo, 1865. 
Munier-Chalmas, Prodrome Vune classification des Rudistes (Journ. de Conchyl. vol. XXI.), 1873.— 
White, C. A., Bull. U.S. Geol. Surv., No. 4, 1884; No. 22, 1885.—Dowvillé, H., Bull. Soc. Géol. 
France [5], XIV. p. 389; XV. p. 756; XVI. p: 699; XVII. p. 627; XVIII. p. 324; XIX. p. 
506 ; 1886-91.—di Stefano, G., Studii stratigratici e paleontologici sul systema cretaceo di Sicilia. 
I. Gli Strati con Caprotina. Palermo, 1888.—Douwvillé, H., Etudes sur les Rudistes (Mem. Soe. Géol. 
France. Paléontologie, I.-III.), 1890-93. 

