rRlBE NAYADES 223 



IRIDINA. 



Equivalve, inequilateral, transverse ; beak small, turned to one side 

 and nearly straight ; two separate lateral muscular impressions ; 

 hinge long, linear, and attenuated near the centre, tuberculous and 

 nearly ere nated ; tubercles unequal; ligament external and mar- 

 ginal. 



I. Exotica Lam. 1—Bl. t. 66./. 3.—E. t. 204. bis.f \.— W. 

 S. t. 2. f. 10. Transversely elongated oblong, finely striated lon- 

 gitudinally, both extremities rounded, the ventral edge sinuated in 

 the middle ; beaks but slightly projecting above tiie margin. 

 Africa. 



I. Rubens Besh. E. vol. 2. p. 320. — Anodonta R. Lam. 6. — 

 E. t. 201./". 1 Rounded ovate, thick, reddish under a brown epi- 

 dermis ; hinge crenated with obsolete transverse grooves : the 

 sinus of the hinge-margin forming a deep and acute angle. — Nile 2-| 

 I. Nilotica. Ferrussac. $ Sow. Z. J.\. t. 2—W. S. t. 2./. 1— 

 Mytilus Uubius. Gmel. — D.p. 118 Transversely elongated, very 

 inequilateral, posteriorly attenuated, anteriorly produced and broader, 

 cuticle greenish : hinge margin nearly straight, very slightly curved, 

 angulated posteriorly ; toothless but with obsolete irregular undu- 

 lations beneath the umbones : ventral edge slightly incurved sub- 

 centrally : nacre purplish red. — Senaar. 2..5-L 



I. Elongata. Sow. G. — Reeve, t. 92. — Differs from Nilotica 

 chiefly in having its hinge-margin strongly crenated, and its nacre 

 brilliant and pure white. Senegal. 



I. Ovata. Swainson. Phil. Mag. 61.— Reeve, t. 93.— W. S. t. 2. 

 f. 9. — Pleidon Macmurtrei Conrad in Journ A. N. S. Phil. 7. 

 t. 13. Elongated-ovate, strong, convex, ventral edge much ar- 

 cuated, sides rounded, the anterior the broader and longer ; cuticle 

 dark olive with obscure dark bluish green radiating lines , beaks 

 usually eroded; nacre irridescent, silvery but often tinged with 

 pink ; hinge margin subarcuated, becoming broad at the extremities, 

 furnished with large tubercular crenations. 2l. . 3|. Liberia. 



I. Cozlestis. Lea on U. 2. p. 82. t. 22. f. 70 Elongated, sub- 

 cylindrical, very smooth, very inequilateral, thin, straight on the 

 dorsal margin, angular before and rounded behind : beaks somewhat 

 prominent and apparently without undulations at the tip ; cuticle 

 polished, very dark, nacre bluish and irridescent. ly 1 ^* «3f Africa. 

 Margins bubparalltl. 



TRIBE CHAMACEA. 



Shell inequivalve, irregular, and adherent ; hinge with one tooth at 

 most, and with two distinct lateral muscular impressions. 



