Trigonia. mollusc a. TRIG ONI ADtE. 405 



11. 'V.pennata — Oblong, transverse, with concentric costoe; along the 

 middle of the anterior side is a ridge from which many tuberculated ridges 

 diverge each way — Sower. Min. Conch, t. ccxxxvii. f. 6 — In Green Sand. 



] 2. T. elongata — Elongated, gibbose, subtriangular ; anterior side obtuse, 

 transversely costated ; posterior side separated from the anterior by a cre- 



nulated carina, bicariuated, longitudinally striated, striae granulated Sower. 



Min. Conch, t. ccccxxxi. — Upper Oolite. 



13. T. nodosa — Obovate, depressed ; anterior part covered with rows of 

 large knobs, a portion of the posterior pait plain ; superior edge straight.— 

 Sower. Min. Conch, t. Dvii. f. 1. — In Green Sand. 



14. T. imlricata — Transversely oblong, depressed ; with five or six con- 

 centric dentated, subimbricated keels upon the rounded anterior side ; pos- 

 terior side obliquely truncated, ribbed. — Sower. Min. Conch, t. Dvii. f. 2, 3. 

 — Oolite. 



15. T. cuspidata. — Obovate, depressed, ribbed ; posterior side truncated, 

 its lower angle pointed ; ribs concentric, with projecting angles where they 

 pass into the posterior side. — Sower. Min. Conch, t. Dvii. — Oolite. 



16. T. angulata — Transversely elongated, convex ; posterior side produced, 

 truncated, transversely striated, bounded by a ci'enulated line ; the remain- 

 der ornamented with nodose ridges, bent at right angles as they pass over the 

 middle — Sower. Min. Conch, t. Dviii. f. I.— Under Oolite. 



17. T. prf^Ms—Obovato-triangular, with transverse smooth ribs ; posterior 

 side obliquely truncated, marked with several crenulated ridges, and bound- 

 ed by a strong crenulated keel ; lunette large, regularly striated across. — 

 Sower. Min, Conch, t. Dviii. f. 2, 3 — In Oolite. 



18. T. speclabilis. — Suborbicular, rather elongated, convex, nearly smooth, 

 ornamented with about seven bent rows of large round tubercles upon the 

 anterior side, and a few small ones scattered over the posterior side ; one row 

 of compressed tubercles upon the posterior slope. — Sower. Min. Conch. t.Dxliv. 

 — In Green Sand. 



Gen. CI. AVICULA. — Shell flat, oblique unequivalve, un- 

 equilateral ; transversely produced in a straight line at the 

 base, where the sides are lobed, and the beaks rather re- 

 mote ; hinge linear, with a single tooth in each valve un- 

 der the beaks ; ligament linear external. 



412. A. Mrundo. — With the tail as long as the wing. 



Turt. Biv. Brit. 220, t. xvi. f. 3 — On the southern coasts of England 

 and Ireland. 

 Length 2 inches, breadth nearly the same ; smooth, or slightly scaly with 

 the layers of growth, but, under a lens, it appears finely punctured ; colour 

 green or brown ; inside pearly. It was'first observed, as a native, by Miss 

 Hutchins, in Bantry Bay ; and announced as British by Mr Sowerby in his 

 Min. Conch, i. 14. 



EXTINCT SPECIES. 



1. A. jnerfia.— Ovate, depressed ; wings large unequal, one wing acute, 

 valves nearly equal ; length of the shell and hinge nearly equal ; surface 

 smooth. — Sower. Min. Conch, t. ii London Clay. 



