356 VENERID^E. 



brown ; the upper pair do not cover the lower, and they are 

 decussated on both surfaces by the network of the circulatory 

 vessels: palps small, triangular, striated on the inner, and 

 smooth on the outer surface : foot muscular, slightly bent or 

 geniculated, and lance-shaped. 



SHELL rhomboid-oval, moderately convex, solid and opaque, 

 not so glossy as the last species : sculpture, numerous and 

 close-set flattened concentric bands, which are divided by 

 faintly impressed lines, so that the shell appears to be grooved 

 or tooled rather than ribbed ; these bands occasionally dicho- 

 tomize or branch off, and are much stronger and more raised 

 (becoming laminar) on the posterior side ; they are crossed by 

 fine, irregular, but equally numerous longitudinal striee decus- 

 sating the surface ; the microscopical markings are also pre- 

 sent : colour yellowish-white, often variegated by reddish- 

 brown rays, zigzag streaks, or blotches of every conceivable 

 width, shade, number, and form, sometimes tinged with pur- 

 ple, umber, or the darkest brown, occasionally yellowish or 

 pure white : epidermis horncolour, fibrous, seldom persistent 

 in any part : margins nearly straight or but little bent in front, 

 trending upwards with a sharper curve to the anterior end, 

 which is rounded and terminated behind by an excavation for 

 the lunule, produced and obliquely truncate at the posterior 

 side, the end of which is rounded, straight and horizontal on 

 the dorsal side in the young but sloping gradually in the adult : 

 beaks small, somewhat recurved, and close to each other ; um- 

 bonal area rather prominent : lunule lanceolate, deep but not 

 very distinct, nearly smooth, mostly of a darker hue : corselet 

 narrow, defined on each side by the edges of the ligamental 

 groove : ligament rather long, yellowish -brown or horncolour, 

 wholly exposed and projecting beyond the lips of the corselet, 

 contained in a marginal groove, minutely striated across when 

 fractured, showing its compact structure and tendinous tissue : 

 hinge-line representing a very obtuse angle : hinge-plate solid 

 but not very broad except under the beak, where it forms a 

 kind of shelf: teeth, in the right valve three erect, slender, 

 parallel, and nearly equal-sized cardinals, the posterior of which 

 is rather the smallest, and the other two are double or bifid 

 at the crown ; the left valve has the same number and kind 

 of cardinals, the anterior being the smallest, and the others 

 double ; laterals ridge-like and indistinct : inside towards the 

 beaks porcellanous, and covered with minute and irregularly 

 confluent tubercles, pure white or stained with purple at the 



