MACTRA. 425 



The fry are oval and very tumid. M . solida resembles in 

 form and size the variety cinerea of the present species ; 

 but, besides being natter and thicker, it invariably has 

 strong transverse grooves on each side of the beak. 



I cannot think why Linne gave such an unpolite name 

 to this species — unless it originated in a philosopher's 

 joke, like that attributed to the derivation of Assiminia. 

 It is the Trigonella radiata of Da Costa ; and the variety 

 is probably the M. coralUna of Buonanni and Linne, 

 and the M . siraminea of Lamarck. 



4. M. glau'ca*, Born. 



M. qlauca, Born, Test. Mus. C;es. Vind. p. 51, t.3. f. 11, 12. M. helvacea, 

 F. & H. i. p. 366, pi. xxiii. f. 2. 



Body white, the posterior side and tubes being tinged with 

 golden yellow : mantle delicately fringed with short flake- 

 white filaments ; edges projecting beyond the valves : tabes 

 conical and rather short, extending about an inch, of equal 

 length and diameter, streaked lengthwise with rufous-brown ; 

 orifices encircled with short and unequal cirri of the same 

 colour. 



Shell triangularly oval, convex but not ventricose, ex- 

 panded and gradually sloping from the umbones to the mar- 

 gins, thin for its size, and glossy under the epidermis : sculp- 

 ture, numerous delicate and minute concentric striae, as in 

 M. stultorum, and occasional lines of growth : colour yellowish- 

 white, variegated by longitudinal rays of yellowish -brown or 

 fawncolour, arranged as in the last species, and of a brighter 

 hue at the beaks, besides a large stain of chestnut on the dorsal 

 margins : epidermis light brown, fibrous, glistening like fine 

 satin in front and on the anterior side, coarser on the posterior 

 side : margins scarcely (if at all) curved on the ventral side, 

 and obliquely sloping backwards to the anterior end, which 

 is rounded with a tendency to angularity, bluntly angular 

 and much broader on the posterior side, where there is a 

 considerable gape and an obscure ridge from the beak to 

 the angular point in each valve ; dorsal margins very gently 



* Bluish-grey. 



