406 MOLLUSCA. TRIGONIADtE. Pijjna 



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

 valve ; flatter valve smooth, Avith the anterioi- ear pointed. — Sower. Min. 

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



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

 costse ; ears nearly equal ; shalloAV 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 costte ; flatter valve convex. 



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



Sower. INIin. Conch, t. ccxliv, f. 2. — Middle Oolite. 



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



hinge-line long, Ibrnung part of the posterior wing, which is most distant 



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



G. A. lanceolata Transversely linear; lanceolate, compressed; posterior 



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

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



Gen. CII. PINNA. — Shell longitudinal, cuneiform, equivalve; 

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

 linear, very long, and subinternal. 



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

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



Penn. Brit. Zool. iv. 115. Mmit. Test. Brit. 180.— P. Isevis, Don. Brit. 



Shells, t. clii P. ingens and fragilis, Turt. Biv. Brit. 222. t. xxii. tl 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 fii'st discovered, as British, by the late 



Dr AValker. IMontagu found it gregarious in beds, left dry at very low tides 

 in Salcomb Bay. 



414. V.Jragilis. — Shell triangular ; front margin rounded ; 



scaly ; ribs about eighteen. 



Penn. Brit. Zool. iv. 114, t. Ixix. f. 80 P. niuricata, 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. 



Pult. Dorset. 39 Mont. Test. Brit, 183. t. v. f. 3 — Turt. Biv. Brit. 224. 



— Dredged near Weymouth. 



