244 TESTACEOUS MOLI1.USCA. 
M. Macexsanicus. Chem. 742,3.—Lam. 1.—E. t. 217. f. 2. 
—M. Bivens. D. p. 313.—W. t. 12. f. 28.— Knorr. 4. t. 30. f. 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 
nithin. | 
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 striz 
decussating the radiating sulci. 25.—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. Varicty. Narrower and the posterior ventral edge 
quite flat. 14. New Helland. 
M. Exustus Lin. Mus. Ulric. 540.—Lam. 6.—D. p. 308.— List. 
366. f. 206.—E. t. 220. f. 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. 3..14.—W 
Indies. 
M. Birnocuraris. Lin. Mus. 540.— Lin Sys. 1156.—D. p. 307,— 
Lam. 7.—Ch. 736. 7.—E. 218. f. 5.—W. t. 12. f. 17.—Ticno- 
conta B. Wieg. 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 

1M. Deshayes considers as varieties of this species 
M. Crenatus Lam. 3.—E. 217. f. 3.—Son. 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.—Fav. t. 50. f. Re. 1. Ovate-trian- 
gular, longitudinally suleated, decussated by unequal transverse 
striz ; livid purple under a blackish epidermis ; beaks acute, cur- 
ved and channelled on the inner side. 44.—America. 
