Pectunculus. mollusc a. ARCADE. 
401 
EXTINCT SPECIES. 
1. P. decussatus — Transversely obovate ; sides rather straight ; surface 
covered with numerous longitudinal strise ; hinge teeth 25 to 30 ; margin 
thick, plain. — Sower. Min. Conch, t. xxvii. f. 1. — London Clay. 
2. costatus. — 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. Plumstediensis . — Transversely obovate, slightly oblique, with longi- 
tudinal obscure furrows, and minute transverse striae ; margin serrated with- 
in — Sower. Min. Conch, t. xxvii. f. Z.-^Plastic Clay. 
4. P. variaUlis . — 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, 
t. cccclxxii. f. 1. — London Clay.- 
6. 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. sublcBvis — Transversely obovate, equilateral, rather gibbose, with 
many slightly'elevated ribs ; beaks short, nearly close ; sides smooth — Sower. 
Min. Conch, t. cccclxxii. f. 2 — In Ch'een 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.— -/Sbzwr. 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. nuclea . — Shell subtriangular ; beak near the short 
end with an oval impression beneath. 
Area nucleus, Linn. Syst. i. 1143. Pemi. Brit. Zool. iv. 98. Mont. Test. 
Brit. 141 — N. nucleus, Turt. Biv. Brit. 170, t. xiii. f. 4 — Not un- 
common. 
c c 
VOL. I. 
