Trigonia. MOLLUSCA. TRIGONIAD^. 405 



11. T. pennata Oblong, transverse, with concentric costae; 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. 



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



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

 nulated carina, bicarinated, longitudinally striated, striae granulated— Sower. 

 Mill. Conch, t. ccccxxxi — Upper Oolite. 



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



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

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



14. T. imbricata. — 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. £ 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 crenulated 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. 



]7- T. pullus.-— 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. — 

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



18. T. spectabilis. — 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. hirundo. — 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. media.— Ovate, depressed ; wings large unequal, one wing acute, 

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

 smooth— Soim - . Min. Conch, t. ii.— London Clay. 



