ACEPHALA. 439 
length about equal, surface somewhat squamous near edge; colour 
blue-black ; valves nearly flat, right one most so; auricle very small 
triangular ; dorsal edge straight, a little produced at tip ; posterior edge 
emarginate near summit, then descending, curves gently forwards ; 
basal edge slightly curved; anterior edge circularly rounded ; deeply 
emarginate below ear; byssus-notch deep, fissure-like, edge crenulate ; 
byssus tubercle very small. Nacre bluish-white; the dark purplish- 
black substance extending far beyond; no visible teeth. 
Length two inches and three-fourths; height two inches; breadth 
half an inch. 
Dredged at Singapore. 
More like A. margaritifera in form than any other, but is less 
retuse, destitute of scales, and having its substance a plain purplish- 
black. It belongs to Lamarck’s genus Meleagrina, which is now 
justly regarded as only a subdivision of Avicula. 
Figure 554, the shell. 
AvicuLa vipua (Gould). 
T. parva, tenuis, dolabriformis, viz obliqua, per-inequilaterals, mutica, 
nitens, ex viridi purpurascens, deinde nigra, albo obscuré radiata: 
valva dextra planulata: valva sinistra convexa, ecaudata: auricula 
parva, triangularis ; fissura parva, super ficialis, edentata: margarita 
ex argenteo violacescens ; limbo lato, nigro. 
Avicula vidua, Goutp; Proceed. Boston Soc. Nat. Hist., ii. 309. 
Noy. 1850. Expedition Shells, 89. 
SHELL small, thin, fragile, slightly oblique, length and height 
about equal; surface smooth, purplish-black, with indistinct white 
radiations; in its early stages grass-green radiated with white; left 
valve angularly convex; right valve flat; dorsal margin not caudate, but 
a little emarginate at posterior edge; auricle very small, triangular ; 
re-entering angle very obtuse, notch small and shallow ; cardinal edge 
broad; no perceptible teeth. Nacre bluish-silvery, darker at peri- 
phery, nearly semicircular, calcareous edge very broad, black and 
