244 TESTACE0T7S M0L1.USCA. 



M. Magellanicus. Chew. 742,3. — Law. \.—E. t. 217. /. 2. 

 — M. Bidens. D. p. 313.— W. t. 12./. 28.— Kttorr. 4. t. 30.'/ 3 

 Oblong with thick raised longitudinal wavy sulci ; shell thick, white 

 at the beaks, becoming purple at the posterior ventral, cuticle pur- 

 plish brown or maroon ; hinge margin forming a more or less 

 distinct angle with the anterior ; posterior ventral edge usually 

 nearly straight ; beaks acute and scarcely curved ; hinge with but 

 one tooth : margin crenated. 5. Magellan. Beaks slightly channelled 

 within. l 



M. Erosus. Lam. 2. Elongated-oblong, angulated, scarcely 

 dilated and usually eroded at the dorsal angle, anteriorly depressed : 

 dark purple both within and without : crowded concentric striae 

 decussating the radiating sulci. 2j. — New Holland, generally 

 deformed. 



M. Hirsutus. Lam. 5. Subtriangular, gaping and rather flat- 

 tened posteriorly, the longitudinal grooves fine, covered with a 

 reddish brown bearded epidermis: ligament broad, beaks much 

 curved and well defined, the margins crenulated : inside livid but 

 irrediscent. Variety. Narrower and the posterior ventral edge 

 quite flat. \\. New Holland. 



M. Exustus Lin. Mus. Ulric. 540. — Lam. 6. — D.p. 308. — List. 

 366./. 206.— E. t. 220. / 4. Oblong, with numerous fine radia- 

 ting slightly elevated sulci, which are at least as narrow as the 

 interstices, of a livid purple under a glossy yellow epidermis, co- 

 vered by which its colour is that of scorched paper ; hinge margin 

 short, forming a distinct angle with the anterior : posterior ventral 

 edge swelling out near the rounded beaks : a few tooth-like crenula- 

 tions at the extremity of the hinge margin : hinge with two teeth in 

 one valve. Var. Narrower and scarcely angulated. -|..li. — W 

 Indies. 



M. Bilocularis. Lin. Mas. 540. — Lin Sys. 1156. — D.p. 307, — 

 Lam. l.—Ch. 736. l.—E. 218./ 5.— W. t. 12. / 17.— Ticho- 

 gonia B. JVieg. Arc. 1837. p. 48, Ovate triangular, posteriorly 

 flattened (incurved by age) ; hinge margin short, with, internal 

 tooth-like crenations ; colour variable, under a bright green epider- 

 mis, often purplish, blue or dull crimson, rayed with numerous 



1 M. Deshayes considers as varieties of this species 

 M. Crenatus Lam. 3.—E. 217. / 3.— Sow. G. f. 3. Ovate- 

 triangular, thin, with radiating sulci, purplish violet, white at the 

 posterior ventral edge : margin crenated. 3£. — Carolina.? 



M. Decussatus. Law. 4. — Far. t. 50. / r. 1. Ovate-trian- 

 gular, longitudinally sulcated, decussated by unequal transverse 

 striae ; livid purple under a blackish epidermis ; beaks acute, cur- 

 ved and channelled on the inner side. 4^. — America. 



