Pectunculus. MOLLUSCA. ARCADE. 401 



EXTINCT SPECIES. 



1. P. decussatus Transversely obovate ; sides rather straight ; surface 



covered with numerous longitudinal striae ; hinge teeth 25 to 30 ; margin 

 thick, plain. — Sower. Min. Conch, t. xxvii. f. 1. — London Clay. 



2. coslatus. — Orbicular, depressed, with 25 longitudinal sharp ridges, and a 

 few transverse striae ; hinge of 14 teeth ; margin serrated within— {Area de- 

 ieta of Brander. Sower. Min. Conch, t. xxvii. f. 2 — London Clay. 



3. P. Plumslediensis. — Transversely obovate, slightly oblique, with longi- 

 tudinal obscure furrows, and minute transverse striae ; margin serrated with- 

 in Sower. Min. Conch, t. xxvii. f. 3 — Plastic Clay. 



4. P. variabilis. — Obliquely suborbicular, rather convex, finely striated 

 longitudinally, becoming smooth or sulcated by wear ; teeth of the hinge 

 and lines upon the area of the ligament, numerous ; beaks short, nearly close. 



— Sower. Min. Conch, t. cccclxxi. f. 1 — In Crag It is probable that this shell 



is merely the Pectunculus pilosus, found in modern marine diluvium, instead of 

 a species connected with the anterior epoch. 



5. P. brevirostris. — Transversely obovate, rather oblique, and inequilate- 

 ral, convex, obscurely costated, concentrically striated ; hinge line rather 

 straight ; beaks short, not oblique ; hinge teeth few. — Sower. Min. Conch. 

 1. cccclxxii. f. 1 — London Clay. 



C. P. scalaris Obovate, convex, longitudinally ribbed, ribs narrow, sharp, 



area of the ligament short, projecting at the extremities, with a triangular 

 pit in its centre ; margin irregularly toothed. — Sower. Min. Conch, t. clxxii. 

 f. 2. — London Clay. 



7. P. sublcevis — Transversely obovate, equilateral, rather gibbose, with 

 many slightly 'elevated ribs ; beaks short, nearly close ; sides smooth.— Sower. 

 Min. Conch, t. cccclxxii. f. 2 In Green Sand. 



8. P. umbonatus. — Orbicular, gibbose, nearly equilateral, longitudinally 

 striated and obscurely costated ; beaks prominent, obliquely curved, a lobe 

 on the anterior side— Cardium umbonatum, Sower. Min. Conch, t. clvi. f. 2, 

 3, 4, and P. umb. ib. t. cccclxxii. f. 3. — In Green Sand. 



9. P. minimus Orbicular, convex, smooth ; hinge line straight, promi- 

 nent at the extremities ; margin not toothed — Sower. Min. Conch, t. cccclxxii. 

 f. 5— In Oolite. 



10. P. oblongus. — Transversely oblong, inequilateral, rather convex, smooth; 

 sides obliquely truncated; margin not toothed.^-Swer. Min. Conch, t. cccclxxi. 

 f. 6 In Oolite. 



Gen. C. NUCULA. — Shell inequilateral, beaks approximate ; 

 hinge line bent in the middle, with a spoon-shaped pro- 

 jecting tooth at the angle, and numerous lateral sharp- 

 pointed teeth ; ligament internal. 



* Margin crenulated. 



— 408. N. nucha. — Shell subtriangular ; beak near the short 



end with an oval impression beneath. 



Area nucleus, Linn. Syst. i. 1143. Penn. Brit. Zool. iv. 1)8. Mont, Test. 

 Brit. 141 — N. nucleus, Turt. Biv. Brit. 176, t. xiii. f. 4 — Not un- 

 common. 



VOL. I. C C 



