224 TESTACEOUS MOLLUSCA. 
the anterior slope: nacre white, bluish anteriorly. 15..3.— 
hio. 
A. Sinvosa. Lam. 14.—Z#. t. 203. f. 2. Oval, transversely 
striated, contracted at the ventral margin, hinge margin waved and 
sinuous, being concave at the posterior extremity, with whose edge it 
forms a sharp angle: beaks moderately prominent, smooth, and 
spotted with violet : brilliant and irridescent within. 34. 
A. Exttis. Lea. on U.2. p. 81. t. 22. f.68. Wide, very much 
compressed, very thin, slender, rounded and very short posteriorly, 
produced and angulated anteriorly: beaks scarcely prominent ; 
ligament long and thin; cuticle smooth brown, apparently rayless : 
nacre bluish and iridescent. 13.. 62. 
A. Tenesricosa. Lea. in Am. Ph. Tr. 1837. t. 12. f. 36.— 
D’ Orb. in Mag. de Z. 1835. Subelliptic, transverse, thick, 
rounded above and below at both extremities, dorsal line little curved, 
ventral edge incurved in the middle; posterior side short and nar- 
rower, ligament long and thick : cuticle dark olive brown, wrinkled, 
obscurely rayed on the anterior slope ; nacre pearly white, clouded 
with bluish purple, irridescent, with a broad horn-coloured border : 
sinus incurved. 1,3,..33,. R. Parana, S. America. 

1 However closely approximating Anodon, the genus Mycetopus, 
cannot (being subequilateral, ) be strictly included under Lamarck’s 
definition of that genus. 
MYCETOPUS. D’Orsieny. 
Thin, extremely elongated transversely, subarcuated, equivalve, 
subequilateral, gaping at both ends, (chiefly so posteriorly) clothed 
mith an olive green cuticle, bluish internally ; umbones central, 
biangulated, curving inwards: hinge linear, straight, toothless ; 
ligament marginal and thin: muscular impressions rather 
indistinct, compound. 
M. Soutentrormis. D’ Orb. Mag. de Z. 1835. p. 41.— Reeve. 
Sy.t.94. Extremely elongated, subcylindraceous, subarcuated, in- 
flated, thin, rather smooth, greenish brown; beaks central, 
anteriorly rounded ; posteriorly biangulated broad ; ventral edge 
concave ; bluish within. 2..9.— Bolivar. 
M. Sitiquosus. D’Orb. in Mag. de Z. 1835.—Anopon 8. 
Spix. Test. Braz. t. 23. f. 2.—A. Loneinum. Spix.t. 22. f. 2. 
A. Pyemaun. t. 23. f. 34. Elongated, compressed, straight, 
extremely thin, smooth, pellucid, yellowish green ; beaks thrice as 
near the posterior as the anterior, anteriorly truncated and rounded, 
posteriorly long and broad, subrhomboidal; ventral edge convex : 
inside bluish white. 14..6.— Bolivar. 
