lucinopsis. 363 



mentioned families. The microscopical strise, charac- 

 teristic of the shells of the Veneridce, are absent in 

 Lucinopsis. In its general appearance this genus agrees 

 with Lucina ; but the recurved beaks, sinuation of the 

 pallial scar, and length of the tubes offer conclusive 

 reasons for their separation. 



Lucinopsis unda'ta *, Pennant. 



Venus undata, Penn. Brit. Zool. p. 95, pi. 55. f. 51. L. undata, F. & II. 

 i. p. 435, pi. xxviii. f. 1, 2, and (animal) pi. M. f. 2. 



Body milk-white, or of a pale pinkish drabcolour : mantle 

 having its edges wavy, or sometimes partially jagged, but 

 never serrated or fringed ; ventral opening small : tides more 

 or less divergent, occasionally tinged with orange, conical, 

 capable of being considerably extended ; incurrent tube the 

 smaller in diameter, but longer of the two, its orifice margined 

 by a circle of very short and minute dark specks, and fringed 

 with 16-20 white cirri of various sizes and lengths ; excurrent 

 tube having its orifice encircled with 12-15 white cirri, which 

 are uniformly short and without the marginal row of dark 

 specks : gills pale drab, the upper plates being much smaller 

 than the lower and half overlapping them ; pectinations rather 

 fine, but not very distinct : palps of the same colour as the 

 gills, fleshy, rather long, triangular, pointed, strongly striated 

 on the outside and smooth within : foot of moderate size, white, 

 flat, pointed, not much bent, destitute of a byssal groove, and 

 issuing from the front or ventral side. 



Shell almost circular, tumid, semitransparent, rather glossy: 

 sculpture, numerous and fine, but irregular, concentric striae, 

 and occasional lines of growth : colour milk-white, with often 

 a yellow or ochreous hue, especially near the beaks : epidermis 

 thin, like varnish and slightly iridescent, longitudinally (but 

 very minutely) striated or puckered: margins more or less 

 straight on the ventral side in the adult and rounded in the 

 young, regularly curved on the anterior side, excavated below 

 the beaks, obtusely angular at the posterior end, with an 

 abrupt slope or truncation on that side ; dorsal or ligamental 

 margin very gently curved in the adult and sloping in the 



* Wavy. 



r2 



