TRIBE MAI.LKACKA. 261 



linear, usually much distorted, straight or curved, flattened, fra- 

 gile : white, tinged with reddish violet, margins of the sides sub- 

 parallel, base retuse, slightly winged on one side, obsoletely mu- 

 cronated. 3. Timor and Nicobar Isles. Allied to the last. 



M. Decurtatus. Lam. 6. — Del. t. 14. f. 6. Small, oval or 

 oblong, flattened, fragile; base variable, ligamental pit very short. 

 — Australia. 



AVICULA. 



Shell inequivalve, fragile, not externally foliaceous, with the dorsal 

 margin straight, transverse, and produced at both extremities, the 

 anterior of which is caudiform ; valves oblique, the left one emar 

 ginate, with a sinus or notch, through which the byssus passes ; 

 hinge linear, with one tooth on each valve under the beaks ; liga- 

 ment linear and marginal, placed in a long narrow groove, not 

 traversed by the byssus. 



A. Macroptera. Lam. — Mytilus Hirundo var. D. Gmel. 

 — Gualt. t. 94. A — Kn. 6. t. 2. Very large, blackish brown (when 

 very young, with whitish rays) ; wing very ample, obliquely curved, 

 tail rather long and almost linear at its termination, body extremely 

 elongated, within pearly, becoming reddish by age. — Var. A 

 Lotorium. Lam. 2. — With the tail very short. 7. — W. Indies. 



A. Semisagitta. Lam. 3. — List. t. 220. /. 55. — Kn. 4. t. 8. 

 /. 5.- A Macroptera Jun. Bl. t. 63. f. 3. Black or reddish 

 yellow, body short and very oblique; the ears oblique, equal, pro- 

 minent, subventricose, the tail long. — Var. Reddish yellow, obso- 

 letely rayed with brown. — Australia. — Africa 1 



A. Heteroptera. Lam. 4. — Del. t. 14. f. 7. Yellowish or 

 reddish, transversely elongated, the posterior lobe having the shape 

 of a spear point and very oblique; one valve anteriorly shorter 

 than the other : tail elongated. — Var. Blackish with the wing 

 less oblique. — Red Sea ? 



A. Crocea. Lam. 6. — Glabrous, uniform orange yellow, pos- 

 terior appendage obliquely diverging. Var, A. Rump. t. 46. G ? 

 Rich orange, the hinge margin extremely elongated so that the tail 

 is long and acute, the body being short and narrow : posterior ap- 

 pendage rather large, the sinus nearly rectangular. Var. B. Tail 

 short, not longer than the posterior wing. Var. C. Avicula 

 Chinensis. Leach. Z. M. 2. t. 114. Citron yellow, the tail 

 short. — Isle of France, (for A and B.) * 



1 M. Deshayes states that the Falcata of Lam. 5, is the same 

 species as Tarentina. 



