304 MALACOZOA. TROPIOPODA. LAMELLIBRANCHIAT1, 



very convex, with the umbo prominent ; both valves concen- 

 trically striato-sulcate, the left, or smaller, with radiating 

 raised lines ; the epidermis yellow or brown ; the hinge nearly 

 central, both margins sloping; the anterior end rounded, the 

 posterior narrowed, and truncato-angular. Length five- 

 twelfths of an inch, height four- twelfths. 



Not uncommon on hard ground in rather deep water ; fre- 

 quently brought up by the lines. 



Mya inaequivalvis. Mont. Test. Brit. 38. PI. 26. f. 7. Mya 

 insequivalvis. Penn. Brit. Zool. ; Ed.n. iv. 166. Corbula Nucleus. 

 Lamk. Syst.v.496; Ed.n.vi. 139. Corbula Nucleus. Turt.Brit. 

 Biv. 39. PI. 3. f. 8, 9, 10. Corbula striata. Flern. Brit. Anim. 

 426. -Cardrum striatum. Walker, Test. Miu. 24. f. 85. 



FAMILY XII. PHOLADINA. 



Animal spherical, oblong, or vermiform, having the 

 mantle closed and more or less tubular, with an an- 

 terior aperture for the foot, which is small; two ge- 

 nerally elongated tubes, coherent, the upper for the 

 passage of the excrement, the lower for respiration ; the 

 labial appendages small; the branchiae elongated, ex- 

 tending into the siphon. 



Shell generally bare, white, more or less elongated, 

 sometimes nearly spherical, often truncated, equivalve, 

 inequilateral, open at both ends, more widely before ; 

 hinge toothless ; ligament seldom conspicuous, some- 

 times replaced by appendages of the mantle ; muscular 

 impressions well marked, connected by a distinct pallial 

 impression, which is deeply excavated behind. 



The species, which are marine, reside in rocks, stones, 

 wood, sand or mud, in cavities from which they are in- 

 capable of emerging. They have frequently a calcareous 

 tube, which is prolonged backwards, or sometimes have 

 the shell furnished with accessory pieces for closing it 

 more completely. 



GENUS 1. PIIOLAS. BORER, OR PIDDOCK. 



Animal subovate or oblong, with the mantle reflected 

 above to connect the valves and accessory pieces, there 

 being no ligament ; its anterior aperture rather small ; 



