208 



CONCHIFERA. 



Cyrena. 



3. Cyprina eqdalis. — The Equal Cyprina, pi. LXXXV. 

 fig- 7. 



Venus equalis. Sowerby, I. p. 59, pi. 21. 



Sub-orbicular, convex ; beaks obtuse, incurved ; hinge very 

 strong ; surface covered with numerous concentric striae, and 

 a few shallow lines of growth ; substance of the shell very 

 thick. 



From the Crag, Suffolk. 



4. Cyprina planata. — The Plain Cyprina, pi. LXXXV. 

 fig. 8. 



C. planata. Sowerby, VII. pi. 619. 



Nearly orbicular and sub-cordiform ; gibbose ; beaks ob- 

 tuse ; on the posterior side a furrow, emanating from the back 

 of the beaks, terminates on the margin ; surface with shallow, 

 unequal lines of growth. 



The London Clay, Nuneham, Brentford, and Bracklesham. 



5. Cyprina Morrisii. — Morris's Cyprina, pi. LXXXVI. 

 fig- 17. 



C. Morrisii. Sowerby, VII. pi. 620, fig. 1. 



Sub-orbicular ; moderately gibbose ; beaks obtuse, incurved ; 

 surface with shallow concentric lines of growth ; back rather 

 straight ; base arcuated. 



The London Clay, Heme Bay, Watford, Plumstead, and 

 Reading. 



6. Cyprina angulata. — The Angulated Cyprina, pi. 

 LXXXV. fig. 10. 



Venus angulata. Sowerby, I. p. 145, pi. 65. 



Transversely ovate ; beaks short, very obtuse, and incurved ; 

 anterior side with a slight longitudinal ridge, and a very little 

 truncated ; surface smooth. 



The Greensand, Blackdown. 



7. Cyprina transversa. — The Transverse Cyprina, pi. 

 XXXV. fig. 3. 



C. Morrisii. Var. Sowerby, VII. pi. 620, figs. 2, 3. 



Transversely ovate, gibbose ; beaks obtuse, slightly incurv- 

 ed ; anterior side short and rounded ; posterior side elon^'ated ; 

 back arcuated, and bending suddenly downwards, forming an 

 angle whore it meets the basal line ; an elevation extends from 

 the beaks to the posterior margin ; surface smooth, with un- 

 equal shallow lines of growth. 



The London Clay, Watford. 



8. Cyprina rostrata. — The Beaked Cyprina, pi. 

 LXXXVI. fig. 18. 



C. rostrata. Sowerby, Geo. Tr. 2d Sor. IV. p. 341, pi. 17, 

 fig. 1. 



Obliquely triangular ; beaks large, much produced, and in- 

 curved, projecting nearly in a line with the margin, and under 

 them the side is very concave, hollow ; dorsal line very little 

 curved ; posterior side considerably lengthened, and narrowed 

 at the extremity, with a gentle ridge running from the beaks 

 to the margin ; basal line arcuated ; surface rather smooth. 



The Greensand, Blackdown. 



9- Cyprina rustica. — The Rude Cyprina, pi. LXXXVI. 

 fig. 31. 



C. rustica. Sowerby, II. p. 217, pi. 196. 



Sub-orbicular, transverse, gibbose ; beaks obtuse, a concave 

 space under them ; anterior side narrowed ; dorsal line nearly 

 straight ; anterior side large and rounded ; base arcuated ; 

 surface smooth ; lines of growth rather strongly marked. 



Red Crag, Sutton, and the Coral Crag, Ramshot. 

 10. Cyprina vulgaris. — The Common Venus, pi. 

 LXXXVI. fig. 29. 



C. Tulgaris. Brown, 111. Rec. Conch. Brit. p. 93, pi. 37, 

 fig. 1, and pi. 38, fig. 11. 



Obliquely sub-orbicular, gibbose ; beaks rather large ; sur- 

 face covered with numerous fine, concentric striie ; dorsal and 

 basal line arcuated ; posterior side a little narrowed. 



The Pleistocene Marine Formations, on the Clyde ; and the 

 Coral Crag, Ramshot. 



Sub-Division II.— FLUVIATILE. 



Shell covered with a spurious epidermis, and the hinge 

 provided with lateral teeth. 



Genus XXXIIL— CYRENA.— Zamarcit. 



Shell sub-orbicular, sub-trigonal, equivaJve, ventricose, 

 inequilateral, and solid ; external surface covered with 

 a strong epidermis, and the umbones usually decorticat- 

 ed ; three cardinal, and two remote lateral teeth in each 

 valve ; in one valve the posterior one is situate near the 

 primary teeth, the anterior one being more remote, and placed 

 before the ligament ; in the opposite valve a deep groove 

 intervenes between two teeth, one of which is large, and the 

 other nearly obsolete ; two lateral remote muscular impres- 

 sions ; pallial impression destitute of a sinus; ligament 

 external. 



1. Cy'RENA trigoncla. — The Trigonal Cyrena, pi. 

 LXXXVI. fig. 5. 



Cyrena trigonula. Wood, Mag. Nat. Hist. VII. p. 275, 

 fitj. 45, a and b. 



Ovately trigonal, sub-equilateral, thick, with sub -imbricated 

 transverse lines of growth, with three cardinal teeth in each 

 valve ; lateral teeth largely serrated ; umbones obtuse ; mar- 

 gin plain. 



Found in the Lacustrine Formations at Stutton, where it 

 is very abundant. 



2. Cyrena cy'cladifobme. — The Cyclas-formed Cyrena, 

 pi. LXXXIII. fig. 28. 



C. cycladiformis. Deshayes, Coq. Fos. pi. 19, figs. 7, 8, 9. 

 Ovate ; anterior side rounded, posterior side somewhat 

 acuminated ; surface smooth. 

 The London Clay, Barton. 



3. Cyrena deperdita. — The Lost Cyrena, pi. LXXXVI. 

 fig. 2. 



Cyclas deperdita. (?) Sowerby, III. p. 139, pi. 162, fig. 1. 



Transversely oval, rather gibbose ; umbonate ; anterior side 

 a little angulated ; surface with elevated, irregular lines of 

 growth ; hinge with three bifid cardinal teeth and two lateral 

 ones, which are sometimes striated perpendicularly. 



The Plastic Clay, Charlton and Plumstead. 



4. Cy'rena cuneiformis. — The Wedged-shaped Cyrena, 

 pi. LXXXVI. fig. 3. 



Cyclas cuneiformis. Sowerby, II. p. 140, pi. 172, figs. 2, 3. 



