CYTHERE. 31 



also belongs to the Barton Clay, in which deposit it occurs in greater abundance 

 than in the London Clay. (British Museum.) 



The variety recta (loc. cit., fig. 9) makes a near approach to the next species, 

 No. 36. (British Museum.) 



36. Cythere transenna, 1 sp. nov. Plate II, fig. 12. 



Cytheke angtjlatopoha (non Reuss) . Jones, Monogr. Tert. Entom., 1857, p. 34, 



pi. iv, figs. 17, 18. 

 — scalabis, 3 Jones fy Sherborn. Geol. Mag., 1887, p. 451, pi. xi, fig. 7. 



Another oblong Cythere with nearly equal ends, but the front margin, sloping 

 to the strongly marked anterior hinge, is more oblique than the other. The 

 surface has longitudinal ridges, which on the hinder moiety of the valve are 

 connected by transverse riblets, making irregular square meshes. In their dis- 

 position the ridges vary as to parallelism. 



A fine series of allied forms, from Gaas, near Dax, have been described and 

 figured by Reuss (' Sitz. k. Ak. Wiss. Wien,' vol. lvii, 1868, pp. 38—40, pi. vi, 

 figs. 3, 4, 5, and 7) ; but the differences are sufficiently apparent. 



This species is not uncommon in the Tertiary Sands and Oyster-bed at 

 Colwell Bay, Isle of Wight. Two or three examples are known from the London 

 Clay of Islington. (British Museum.) 



37. Cythere Forbesii, Jones Sf Sherborn. Plate III, figs. 18 a, b. 



Cttheee Fobbesii, Jones fy Sherborn. Geol. Mag., 1887, p. 452. 



A subquadrate form, approaching the more definitely squared Cytherse, for 

 which we keep the convenient subgeneric name of Gythereis. The valves are 

 well rounded in front and behind, with nearly straight lower and upper margins, 

 the latter marked with well-defined hinges. The posterior margin is usually 

 denticulate. The surface bears six or seven crenulate and fenestrate ridges, those 

 on the ventral region being more continuous than those on the dorsal. The 

 interspaces of the ridges are deeply reticulated. 



This distinct and well-defined species we dedicate to the late Edward Forbes, 

 whose investigations in the fossil fauna of the Tertiaries of the Isle of Wight 

 will ever be gratefully remembered. 



1 A lattice before a window. 



2 This name was preoccupied by a species in the ' Challenger Eeport.' 



