TELLTNA. 379 



4. T. te'nuis * Da Costa. 



T. tenuis, Da Costa, Brit. Conch, p. 210; F. &H. i. p. 300, pi. six. f.8, 

 and (animal) pi. K. f. 3. 



Body very flat, yellowish-white : mantle finely fringed : tubes 

 white, nearly equal in length and diameter, the upper one 

 being usually curved upwards : gills two only, one on each side, 

 veiy large and membranous, nearly triangular, most delicately 

 pectinated, and pale brown : palps triangular, not very long or 

 pointed, nor so disproportionately large as in the last species, 

 pectinated more strongly inside than outside, of a sombre hue, 

 marked with paler lines which give them a mottled appear- 

 ance : foot large, broad, compressed, not very pointed, slightly 

 bent. 



Shell triangularly oval, flattened, thin, semitransparent, 

 remarkably glossy and polished ; the right valve is a trifle 

 larger than the left : sculpture, exceedingly slight and indistinct 

 concentric strise, with occasional deeper lines of growth ; the 

 surface is also marked with a few short and obscure longitu- 

 dinal lines : colour white, yellow, flesh, orange, pink, or rose, 

 of various shades, sometimes whitish with a large rosy mark 

 on the umbonal area, or with two divergent streaks of yellow 

 or pink, one on each side of the beaks, or pink with similar 

 whitish rays, or else with transverse bands of a deeper hue : 

 epidermis slight and brilliantly iridescent : margins generally 

 not much curved in front, more so and often bluntly angular 

 on the anterior side, somewhat flexuous on the posterior side 

 and produced to a rather sharp point, from which a slight 

 ridge runs to the beak in each valve, separating the posterior 

 area ; this margin is obliquely truncate ; the dorsal or liga- 

 mental margin has a straight slope to the upper angle of the 

 posterior side : beaks small, nearly straight, scarcely inflected, 

 but turned towards the posterior side : ligament short, but 

 large, very prominent, light horncolour : hinge-line obtusely 

 angular : hinge-plate much broader on the posterior than on 

 the other side, and abruptly truncate at the end of the liga- 

 ment : teeth, cardinals as in the last species ; sometimes the 

 left valve has a posterior, or the right an anterior lateral : in- 

 side glossy, having the same coloured markings as the outside, 

 microscopically wrinkled, and striated towards the margin : 

 pallial scar as in the last species : muscular scars oblong, large 

 and conspicuous. L. 0*65. B. 0-95. 



* Thin. 



