64 MYID-E. 



1. Mya arena'ria"^, Linne. 



M. are?iana, Linn. S. N. p. 1112 ; F. &H. i. p. 108, pi. x. f. 4-6. 



Body fleshy, yellowish-white ; tubular sheath covered by 

 an extension of the ej)idermis of the shell ; orifices of the tubes 

 tinged with red, and fringed with tentacles of different sizes. 



Shell oblong (the right valve a trifle larger than the left, 

 the inequality being more observable in young spe<;imens), 

 equilateral, gaping considerably at both ends, compressed, 

 rather solid, opaque, usually lustreless : sculpture, coarse and 

 irregular concentric striae, diversified by stronger marks of 

 growth : colour ashy-grey, with often a ferruginous tinge, or 

 variegated by radiating Hnes of a brownish hue, which are 

 caused by slight longitudinal folds of the epiderm is : the latter 

 is thin, yellowish brown, fibrous at the sides and in front, and 

 imparting an oblique striation to the surface of the shell : 

 margins rounded on the anterior side, sHghtly curved in front, 

 and wedge -hke on the posterior side ; dorsal margins sloping 

 more on the posterior than anterior side ; posterior side ob- 

 scurely keeled : healcs small, inflected, placed close together, 

 that of the left valve being worn away or broken by continual 

 pressure : cartilage triangular, strong, horncolour : hinge-line 

 almost straight : hinge-plate broad and thick : teeth, in the 

 right valve a slight and oblique cardinal on the anterior side 

 of the cartilage-pit ; the left valve has the complicated process 

 described as one of the characters of the family, which in this 

 species is very large, and irregularly shaped, convex within 

 and concave without; the spur-like flange on the posterior 

 side is placed obliquely, and there is a deep groove next to the 

 hinge-plate for the reception of a blunt tooth-like fold on the 

 same side in the opposite valve: inside chalky-white: scars 

 distinct and deep. L. 2 b. B. 4. 



Yar. lata. Shell dwarfed, more oval and solid. ]\I. lata, 

 J. Sowerby, Min. Conch, t. 81. 



Monstr. Furnished inside with foliaceous plates, showing 

 a laminated structure. 



Habitat : Common on many parts of the coast, at 

 low-water mark ; chiefly in estuaries, where there is an 

 admixture of fresh water with the sea. The variety is 



* Inhabiting sand. 



