406 
MOLLUSCA. TlilGONIAD^. 
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 
costae ; ears nearly equal ; shallow valve nearly flat, with many radii ; ante- 
rior ear large, produced ; posterior ear small — Sower. Min. Conch, t. ccxliv. 
f. -.-.Upper Oolite. 
4. A. incequivalvis. — Oblique, elliptical, convex, with a large projecting ear, 
covered with radiating striae, and many thin costae ; flatter valve convex, 
smooth, marked with diverging sulci, included within the deepest valve. — 
Sower. Min. Conch, t. ccxliv, f. 2. — Middle Oolite. 
5. A. ovata. — Transversely ovate, convex ; posterior side elongated, blunt ; 
hinge-line long, forming part of the posterior wing, which is most distant. — 
Sower. Mill. 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. 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. Mont. Test. Brit. 180. — P. Isevis, 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. INIonlagu found it gregarious in beds, left dry at very low tides 
in Salcomb Bay. 
414. Y .fragilis. — -Shell triangular ; front margin rounded ; 
scaly ; ribs about eighteen. 
Penn. Brit. Zool. iv. 114, t. Ixix. 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; peUucid ; 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. %—Turt. Biv. Brit. 224. 
— Dredged near Weymouth.^ 
