ccxliv 
APPENDIX. 
Species. — C. Rcidiatum. 
Cardium edentulum. Mont. Supple., 29. 
t Mactra radiata. Don., t. 161,. 
Family. — Arcad^e. 
Genus. — Arca. Lam. 
Species. — A. glacialis 
Testa, ovali-elliptica, tenui, villosa, alba, concentric^ et transversim 
striata ; postice rotundata ; umbonibus approximatis ; dentibus sub-obsoletis ; 
margine integerrimo. 
Arca glacialis. Gray, ut supra. 
Shell, thin, oval, elliptical, rounded before and behind, regularly, finely 
concentrically, and transversely striated ; epidermis, silky ; umbones, to- 
wards the joint, incurved, nearly close ; intermediate space, lanceolate, 
ventricose ; margin, even, thin ; hinge-teeth very small, indistinct in the 
middle, rather larger at each end ; length 3-4ths of an inch, depth 3-8ths, 
breadth 4-5ths. 
Animal, mantle lobes separate ; foot flat, compressed, subquadrate, front 
two cut, with one or two fibres from the lower edge : trachea none. 
Family. — Mytilid;e. 
Genus. — Modiola. Lamarck. 
** Shell longitudinally obliquely striated. 
(Modiola Arctica, of Dr. Leach, in Ross's Voyage , is 
Mytilus Fabr., 0. Fab., Fauna Grccnlandica, 419. 
■ Chemnitz, viij., 184. t. 85. f. 761.) 
*** Shell, middle smooth, sinuated, before and behind, generally striated. 
Species I. — Modiola nigra. 
Modiola discrepans. Leach. Ross's Voyage, not of Lamarck, 
Mytilus discrepans. Mont. Ri'it, Shells , t. 26. f. 4* 
Species 2. — Modiola Ice cigala. 
