ORDER in TKLKODKSMACKA 



Carditamera, Conr. Elongated, sub-mytilifonn. /'A /'////< //'*, dun: Small, 

 tM|uilateral, trigonal. CalyptogtnCk^ Dall. Ovoid, .-mouth externally. i'nrilit>ll<i, 

 Smith. Small, with internal ligament. All Tertiary and Kn-.-nt. Tlfmlni, Adam- ; 

 Milneria, Dall. Females with a shelly marsnpimn. 1'cn-nt. 



Superfamily 5. CHAMACEA. Geinitz. 



Carditian forms specialised for a sessile habit, uxno/la n-<th exception a I hi 

 growth, and very unequal valves. Marine. 



Family 9. Chamidae. Lamarrk. 



Shell substance three-fold, the inner layers porcdlannu* and hilmlur, fl>> /////////. 

 obscurely prismatic, the external cellulo-crystalline with reticulated tubules and an 

 spicuous epidermis ; valves unequal, irregular, 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 fixed 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; addm-tor* 

 each composed of two elements. Cretaceous to Eecent. 



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 continual 

 to the point of the beaks, as 

 in other bivalves with, gyrate 

 umbones ; form rounded, 

 attached valve deeper and 

 larger, the free valve natter ; 

 margins usually cross- 

 striated, surface lamellar or 

 spinose ; adductor scars large, 

 not elevated. Cretaceous to 



r ic. 1 10. 



fh,, H u, M^BKWK, Lam. Eocene ; Hampshire. /i- 

 Eocene. 



Echinochama, Fiscli. Nepionic shell elongated, having tin- I'm-m, hinge, and other 

 characters of Cardita ; attached when adolescent, free in the young and adult st 

 Valves sub-equal and similar ; surface vermienlate, spinosi-, with radial ribs. Oligorene 

 and Recent. 



Family 10. Diceratidae. Dall. 1 



Resembling Chama, but with the adductors usually borne on myophoric laminae, or 

 projections which are prolonged into the umbonal cavity below the hinge plate; rii.li->.-; 



1 For the CJtamctcea and Rudistae, Neumayr proposed the term Pachydonta. For special liu-ru- 

 ture see: Ztttd, K. A. DOW, Die Bivalven der Gosaugebilde (Denkschr. Akal.-WisM-n>.-li. \Vit-n, B.l. 

 XXIV.), 1864. Gemmetlaro, <J. G., Caprinellidae della Ciaca dei iutorni di 1'al.Tino, 1865. 

 Mfnii'r-Chalmas, Prodrome d'une classification des Rudistes (Journ. de Couch yl. vol. XXL), 1873. 

 White, C. A., Bull. U.S. Geol. Surv., No. 4, 1884 ; No. 22, ISSG.DowilU, //., Bull. Soc. Gc-ol. 

 France [3], XIV. p. 389 ; XV. p. 756 ; XVI. p. 699 ; XVII. p. 627 ; XVIII. p. 324 ; XIX. p. 

 506 ; 1886-91. di Stefano, G., Studii stratigrafici e paleontologici sul systema cretaceo di Sicilia. 

 I. Gli Strati con Caprotina. Palermo, 1888. Duttrille, If., Etudes >ur U-s Kudistes (Mem. Soc. Gool. 

 France. Paleontologie, I.-IIL), 1890-93. 



