Pectunculus, 



GONCHIFEllA. 



189 



serrated, placed in two rows, one on each side of the umbones, 

 and are separated by a small triangular <li.sk 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 unibones ; two lateral, strongly marked, 

 distant, muscular impressions, which are united by an uninter- 

 rupted pallial impression ; ligament external. 



1. PEtTiNCULi's BKEviRosTRis. — Tlio Sliort-bcaked Pec- 

 tunculus, pi. LXXVII. fig. 1. 



P. brevirostris. Sowerby, V. p. 112. pi. 472, fig. 1 . 



Xearly 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 

 strias, which are invisible without the aid of a glass. 



In the London Clay, Bognor and Reading. 



2. Pectuncul0s pilosds. — The Hairy Pectunculus, pi. 

 LXXVII. fig. 5. 



P. tariabilis. Sowerby V. p. Ill, pi. 471. 



Nearly orbicular, very slightly oblique, and rather convex ; 

 beaks large, rounded, and approximate ; hinge area large, with 

 the triangular lines numerous ; teeth numerous ; surface with 

 fine, wide -set, divergent striie, crossed by remote lines of 

 growth, which become more numerous towards the basal mar- 

 gin. 



In the Plei.stocene Marine Formation, Ayr and Ireland ; the 

 Mammiferous Crag, Thorpe ; the Red Crag, Sutton, and the 

 Coral Crag, Ramshot. 



3. Pectuxcclus obliqdus. — 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 hinge numerous and con- 

 tinuous ; anterior_side a little narrowed ; posterior side con- 

 si<lerably broader ; surface with numerous wide-set, longitudi- 

 nal, divergent striae, crossed by many concentric shallow ones ; 

 marginal crenulations small and numerous ; substance of the 

 shell rather thin. 



The Red Crag, Bromswell. 



4. PectUiN'culus mi.mmus. — The Least Pectunculus, pi. 

 LXXVII. figs. 2, 3, 4. 



P. minimtu. Sowerby, V. p. 114, pi. 472, fig. 5. 



Orbicular ; convex ; equilateral ; hinge-line straight, with 

 about five teeth on each side ; beaks rather prominent ; surface 

 smooth ; destitute of internal martrinal crenulations. 



The Great Oolite, Anclitf, AViltshirc. 



5. PixTUNCULUS oDLONGUs. — Tho Oblong Pectunculus, pi. 

 LXXVII. figs. 6, 7, 8. 



P. ohlotiffui. Sowerby, V. p. 114, pi. 472, fig. 6. 



Transversely ovate ; rather inequilateral and convex ; sides 

 slightly truncated obliquely ; surface smooth, and destitute of 

 internal marginal crenulations. 



The Great Oolite, AnclifT. 



6. Pectunculus delectus. — The Delectible Pectunculus, 

 pi. LXXVII. fig. 13. 



P. coitalui. Sowerby, I. p. 72, pi. 27, fig. 2. 



Orbicular, compressed ; ligaraental area small ; beaks rather 



largo; hinge with about fourteen uninterrupted teeth ; surface 

 with about twenty-five sharp, divergent ribs, and a few con- 

 centric, distant stria; ; margin finely crenulated within. 

 The London Clay, Barton. 



7. Pectunculus decuss.^tus. — The Decussated Pectuncu- 

 lus, pi. LXXVII. fig. 20. 



P. (leciissalui: Sowerby, I. p. 71, pi. 27, fig. 1. 



Sub-orbicular ; sides rather straight ; slightly compressed ; 

 ligamental area small ; hinge with from twenty-five to thirty 

 continuous teeth ; beaks small and obtuse ; surface with nume- 

 rous, very fine, longitudinal, divergent stria3, which are hardly 

 visible without the aid of a lens ; margin thick, and destitute 

 of crenulations. 



The London Clay, Highgate and Bognor. 



8. Pectunculus Plumsteadiensis — The Plumstead Pec- 

 tunculus, pi. LXXVII. fig. 14. 



P. Plumsteadiensis. Suwerby, I. p. 72, pi. 27, fig. 3. 



Sub-orbicular ; slightly oblique ; one side a little straight ; 

 beaks produced ; ligamental area small ; hinge rather straight, 

 with numerous teeth ; surface with obscure, longitudinal, nar- 

 row furrows, with minute concentric stria; ; margin iuternally 

 crenatod. 



The London Clay, Plumstead and Upnor. 



9. Pectunculus cmbonatus. — The Large-beaked Pectun- 

 culus, pi. LXXVII. fig. 11. 



/■•. umhoiuitiis. Sowerby, V. p. <13, pi. 472, fig. 3, and pi. 

 156, figs. 2, 3, 4. 



Xearly orbicular ; almost equilateral and gibbose ; beaks 

 large and prominent, somewhat oblique ; hinge area large, 

 the ligamentary lines triangular ; teeth numerous and con- 

 tinuous ; anterior side a little concave above ; surface with 

 fine longitudinal, radiating striae, and very obscure concentric 

 rilis; inner margin with large crenulations. 



In the Gault at Ridge, South Wiltshire ; and the Green- 

 sand, Blackdown and Ilaldon. 



10. Pectunculus subl^vis. — The Half-smooth Pectun- 

 culus, pi. LXXVII. fig. 10. 



P. siihloevis. Sowerby, V. p. 1 12, pi. 472, fig. 4. 



Almost orbicular, equilateral, and somewhat convex ; an- 

 terior side with a longitudinal depression ; beaks short, ap- 

 proximate, and rounded ; ligamentary S])ace exceedingly 

 narrow ; surface with many obtuse ribs, occupying the centre 

 portion of tho 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. scalarit. Sowerby, V. p. 113, pi. 472, fig. 2. 



Obvate, considerably narrowed above ; the beaks promi- 

 nent ; hinge-line short, angular at the extremities, with a 

 triangular ))it in its centre ; centre of the surface with strong 

 regular ribs ; internal margin with tine irregular crenulations. 



The London Clay, Barton. 



12. Pectunculus Apjoiini. — Apjohn's 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 

 tho beaks ; margin smooth. 



Tho Silurian Limestone, Desertcreat, Tyrone, Ireland. 



