258 MALACOZOA^ TROPIOPODA. LAMELLIBRANCHIATA. 



Hinge very strong, the right valve with a thick promi- 

 nent triangular tooth, and two triangular pits ; left valve 

 with two prominent diverging teeth, and an intervening 

 triangular pit ; lateral teeth merely forming a thickened 

 margin. Ligament external, short, and rather inconspi- 

 cuous. Muscular impressions rather large, elliptical. 

 Pallial impression entire. 



The species of this genus are readily known by their 

 transverse or concentric scaliform rugse, olivaceous epi- 

 dermis, and thick shell. They live in mud, gravel, or 

 sand, in rather deep water. The genus was first named 

 Astarte by Sowerby, afterwards Crassina by Lamarck. 



1. Astarte Danmoniensis. Devonshire Astarte. 



Shell rotundato-trigonal or suborbicular, moderately con vex; 

 with the anterior end shorter, the umbones pointed and ap- 

 proximated ; the dorsal slope very slightly convex, with a 

 narrow-lanceolate, obliquely striated impression, of which the 

 sides slope inwards ; the anterior slope somewhat concave, 

 with a lanceolate, obliquely striated impression having similarly 

 inclined sides ; the valves thick, with twenty or more con- 

 centric, convex ridges, narrower than their interstices, which, 

 as well as they, are concentrically striated ; the epidermis 

 yellowish-brown ; two strong teeth in the left valve, a medial 

 stronger tooth, and two slight teeth in the right; inner surface 

 white ; margin crenate. Length an inch and a-quarter, height 

 an inch. 



Young individuals more compressed, with pale brownish- 

 yellow epidermis. 



Not uncommon in deep water, on hard ground, off the coast, 

 and now and then brought up by the lines. 



Venus Danmonia. Mont. Test. Brit. Suppl. 46. PI. 29. f. 4. 

 Crassina sulcata. Turt. Brit. Biv. 131. PI. 11. f. 1,2. Astarte 

 Danmonia. Flem. Brit. Anim. 440. Crassina Danmoniensis. 

 Lamk. Syst. y.554; 2d Ed. vi. 257. 



2. Astarte Scotica. Scottish Astarte. 



Shell rotundato-trigonal or suborbicular, rather compressed ; 

 with the anterior end shorter, the umbones pointed and ap- 

 proximated ; the dorsal slope very slightly convex, with a 

 narrow-lanceolate, obliquely striated impression, of which the 

 sides slope inwards : the anterior slope somewhat concave, 



