40G MOLLUSCA. TRIGONIAD^E. Pinna 



2. A. echinata. — Obovate, gibbose, many muricated radii Upon the deepest 

 valve; flatter valve smooth, with the anterior ear pointed. — Sower. Min. 

 Conch, t. ccxliii. — In the Inferior Oolite. 



3. A. costata. — Deep valve gibbose, transversely obovate, with eight smooth 

 costse ; ears nearly equal ; shallow valve nearly flat, with many radii ; ante- 

 rior ear large, produced,? posterior ear small — Sower. Min. Conch, t. ccxliv. 

 f. 1. — Upper Oolite. 



4. A. incequivalvis — Oblique, elliptical, convex, with a large projecting ear, 

 covered with radiating striae, and many thin costse ; flatter valve convex. 



smooth, marked with diverging sulci, included within the deepest valve. 



Sower. Min. Conch, t- ccxliv, f. 2. — Middle Oolite. 



5. A. ovala. — Transversely ovate, convex ; posterior side elongated, blunt ; 

 hinge-line long, forming part of the posterior wing, which is most distant. — 

 Sower. Min. Conch, t. Dxii. f. 2 — Inferior Oolite. 



6. A. lanceolata — Transversely linear; lanceolate, compressed; posterior 

 wing large, obtuse angled ; anterior wing minute, pointed. A doubtful shell. 

 Sower. Min. Conch, t. Dcxii. f. 1. — In Lias. 



Gen. CI I. PINNA. — Shell longitudinal, cuneiform, equivalve; 

 pointed at the base ; open at the top ; ligament marginal 

 linear, very long, and subinternal. 



413. P. ingcns. — Shell oval, triangular, with transverse 



arched striae ; flat at top, and straight at the hinder side. 



Penn. Brit. Zool. iv. 1 15. Mont. Test. Brit. 180.— P. laevis, Don. Brit. 

 Shells, t. clii — P. ingens and fragilis, Turt. Biv. Brit. 222. t. xxii. f. 1 . 

 — In deep water on the southern, western, and northern shores. 



Length about a foot, breadth half a foot ; semi-transparent, horn-colour ; 

 compressed at the broad end, from which it runs, in front, nearly with a 

 straight edge, for two-thirds, and then slopes suddenly to the apex ; a few 

 obsolete longitudinal ridges towards the back, and scaly wrinkles towards the 

 front. It is, however, rather irregular in its markings and outline. When 

 examined by a lens, the surface is finely punctured, like the Avicula hirundo. 

 — This species appears to have been first discovered, as British, by the late 

 Dr Walker. Montagu found it gregarious in beds, left dry at very low tides 

 in Salcomb Bay. 



414. Y.JraglUs. — Shell triangular ; front margin rounded ; 



scaly ; ribs about eighteen. 



Penn. Brit. Zool. iv. 114, t. lxix. f. 80.— P. muricata, Don. Brit. Shells, 

 t. x.— P. pectinata, Mont. Test. Brit. 178. Turt. Biv. Brit. 223. t. xix. 

 f. 1 Southern coasts. 



Length six inches, breadth two and a half; pellucid ; corneous ; the longi- 

 tudinal ribs run the whole length of the shell ; towards the middle, in front, 

 the scaly striae run obliquely to the margin. 



415. P. muricata. — Triangular, with ten or twelve broad 



ribs, and intermediate smaller ones at the wide end, beset with 



concave prickles. 



Pnlt. Dorset. 30 — Mont. Test. Brit. 183. t. v. f. 3 — Turt. Biv. Brit. 224. 

 — Dredged near Weymouth. 



