CYTHEREIS. 35 



ventral ridge of spines, which is present in both these forms, is absent, being 

 merely represented by scattered spines, not arranged in a definite order except 



Fig. 3. — Cythereis spiniferrima, sp. nov. Eight valve. "From the London Clay. 



Magnified 20 diam. 



on the anterior area. The reticulation is also much more distinct, — a marked 

 feature in the new form. 



To this same group belongs a rather common, recent and Post-Tertiary 

 species, namely, Cythereis Dunelmensis, Norman (the references are given in full 

 in the ' Monogr. Post-Tert. Entom.,' 1874, p. 168). The chief differences between 

 this and the older form from the London Clay are in the shape of the posterior 

 margin, which is elliptically rounded in the latter instead of being square, and a 

 more definitely spinose, instead of foliaceous, condition of the ornament, 

 especially towards the margins. 



Two valves only ; from the London Clay of Piccadilly. Collected by Messrs. 

 Sherborn and Chapman. (British Museum.) 



9. Cythereis Jonesii, Baird. 



Cythereis ceratoptera (Bosquet). Jones, Monogr. Tert. Entom., 1857, p. 39, 



pi. iv, fig. 1 ; Geol. Mag., 1870, p. 156. 



Dr. G. S. Brady (' Trans. Linn. Soc.,' vol. xxvi, pp. 418 and 476) has merged 

 G. ceratoptera in the recent British species G. Jonesii, Baird, published about the 

 same time as Bosquet's ' Memoire,' 1850-52. (British Museum.) 



10. Cythereis oornuta (Roemer). Plate I, fig. 22. 



Cythereis cornuta (Roemer). Monogr. Tert. Entom., 1857, p. 39, pi. iv, fig. 19 ; 



and pi. v, fig. 15 (omitting the references to 

 lleuss in the synonymy 1 ) ; Geol. Mag., 1870, 

 p. 156; 1887, p. 454. 



This species occurs in the Tertiary sands of Colwell Bay, and in the blue clay 

 of Bracklesham. A very closely allied form is found in the Chalk. 



1 Not C. cornuta, Keuss, in Ilaidinger's ' Nat. Abhandl.,' vol. iii, p. 81, pi. x, fig. 18 a (see 



