PfiCTUNCULUS. 
OONCHIFERA. 
18.9 
serrated, placed in two rows, one on each side of the unibones, 
and are separated by a small triangular disk in each valve, 
which contains the ligament, those of the opposite valves alter¬ 
nately inserted between each other, and becoming nearly obso¬ 
lete towards the umbones; two lateral, strongly marked, 
distant, muscular impressions, which are united by an uninter¬ 
rupted pallia! impression ; ligament external. 
1. Pectunculus brevirostrjs. —The Short-beaked Pcc- 
tnnculus, pi. LXXVII. fig. 1. 
P. brevirostris . Sowerby, V. p. 112. pi. 472, fig. 1. 
Nearly orbicular, slightly oblique, and inequilateral; mode¬ 
rately convex; hinge-line triangular ; teeth few and oblique; 
beaks short, rather obtuse, and approximating, with a slight 
elevation on the anterior side, emanating from the beaks, and 
terminating on the margin, where it projects a little ; surface 
with very flat, longitudinal ribs, crossed by fine concentric 
stria), which are invisible without the aid of a glass. 
In the London Clay, Bognor and Reading. 
2. Pectunculus pilosus. —The Hairy Pectunculus, pi. 
LXXVII. fig. 5. 
P. variabilis. Sowerby V. p, ill, pi. 471. 
Nearly orbicular, very slightly oblique, and rather convex; 
beaks large, rounded, and approximate ; binge area large, with 
the triangular lines numerous; teeth numerous ; surface with 
fine, wide-set, divergent striae, crossed by remote lines of 
growth, which become more numerous towards the basal mar¬ 
gin. 
In the Pleistocene Marine Formation, Ayr and Ireland ; the 
Mammiferous Crag, Thorpe; the Red Crag, Sutton, and the 
Coral Crag, Ramshot. 
3. Pectunculus obliquus. —The Oblique Pectunculus, pi. 
LXXVII. fig. 9. 
Obliquely sub-ovate; somewhat compressed; beaks small, 
rather approximate ; ligament area triangular, with rather 
numerous deep lines; teeth of the binge numerous and con¬ 
tinuous ; anterior side a little narrowed ; posterior sido con¬ 
siderably broader; surface with numerous wide-set, longitudi¬ 
nal, divergent stria}, crossed by many concentric shallow ones; 
marginal creuulations small and numerous ; substance of the 
shell rather thin. 
The Red Crag, Bromswell. 
4. Pectunculus minimus. —The Least Pectunculus, pi. 
LXXVII. figs. 2, 3, 4. 
]\ minimus . Sowerby, V. p. 114, pi. 472, fig. 5. 
Orbicular; convex; equilateral; binge-lino straight, with 
about five teeth on each side ; beaks rather prominent; surface 
smooth ; destitute of internal marginal creuulations. 
The Great Oolite, AuclifF, Wiltshire. 
5. Pectunculus oblongus. —The Oblong Pectunculus, pi. 
LXXVII. figs. 0, 7, 8. 
P. oblongus. Sowerby, V. p. 114, pi. 472, fig. 0. 
Transversely ovate ; rather inequilateral and convex ; sides 
slightly truncated obliquely; surface smooth, and destitute of 
internal marginal creuulations. 
The Great Oolite, Ancliff. 
(i. Pectunculus delectus. —The Delcctible Pectunculus, 
pi. LXXVII. fig. 13. 
P. costalus. Sowerby, I. p. 72, pi. 27, fig. 2. 
Orbicular, compressed ; ligamental area small; beaks rather 
large ; hinge with about fourteen uninterrupted teeth ; surface 
with about twenty-five sharp, divergent ribs, and a few con¬ 
centric, distant strim ; margin finely crenulated within. 
The London Clay, Barton. 
7. Pectunculus decussates. —The Decussated Pectuncu¬ 
lus, pi. LXXVII. fig. 20. 
P. decuseatus. Sowerby, I. p. 71, pi. 27, fig. 1. 
Sub-orbicular; sides rather straight; slightly compressed; 
ligamental area small; binge with from twenty-five to thirty 
continuous teeth ; beaks small and obtuse; surface with nume¬ 
rous, very fine, longitudinal, divergent striae, which are hardly 
visible without the aid of a lens ; margin thick, and destitute 
of erenillations. 
The London Clay, ITighgate and Bognor. 
8. Pectunculus Plumsteadiensis —The Plumstead Pec¬ 
tunculus, pi. LXXVII. fig. 14. 
P. Plumsteadiensis . Sowerby, I. p. 72, pi. 27, fig. 3. 
Sub-orbicular ; slightly oblique ; one side a little straight; 
beaks produced ; ligamental area small; binge rather straight, 
with numerous teeth ; surface with obscure, longitudinal, nar¬ 
row furrows, with minute concentric stria}; margin internally 
crenated. 
The London Clay, Plumstead and Upnor. 
9. Pectunculus umbonatus. —The Large-beaked Pec un- 
culus, pi. LXXVII. fig. 11. 
P. umbonatus . Sowerby, V. p. 113, pi. 472, fig. 3, and pi. 
15 0‘, figs. 2, 3, 4. 
Nearly orbicular ; almost equilateral and gibbose; beaks 
large and prominent, somewhat oblique; hinge area large, 
the ligamentary lines triangular ; teeth numerous and con¬ 
tinuous ; anterior sido a little concave above; surface with 
fine longitudinal, radiating strite, and very obscure concentric 
ribs; inner margin with large creuulations. 
In the Gault at Ridge, South Wiltshire ; and the Green¬ 
sand, Blackdown and Hal don. 
10. Pectunculus subl.evis.— The Half-smooth Pectun¬ 
culus, pi. LXXVII. fig. 10. 
P. sublcecis. Sowerby, V. p. 112, pi. 472, fig. 4. 
Almost orbicular, equilateral, and somewhat convex ; an¬ 
terior side with a longitudinal depression; beaks short, ap¬ 
proximate, and rounded; ligamentary space exceedingly 
narrow; surface with many obtuse ribs, occupying the centre 
portion of the valves, the sides being smooth ; inner edge 
with small crenulations. 
In the Greensand, Blackdown and Lyme Regis. 
11. Pectunculus scalaris.— The Ladder Pectunculus, pi. 
LXXVII. fig. 23. 
P. scalaris. Sowerby, V. p. 113, pi. 472, fig. 2. 
Obvate, considerably narrowed above; the beaks promi¬ 
nent ; biuge-lino short, angular at the extremities, with a 
triangular pit in its centre ; centre of the surface with strong 
regular ribs; internal margin with line irregular crenulations. 
The London Clay, Barton. 
12. Pectunculus Apjohni. —Apjohns Pectunculus. 
P. Apjohni. Portlock, Geo. Sur. p. 429, pi. 34, fig. 8. 
Orbicular, convex; beaks prominent; hinge-line and teeth 
gently arcuated, the teeth more numerous behind than before 
the beaks ; margin smooth. 
The Silurian Limestone, Desertcreat, Tyrone, Ireland. 
