GERVILLIA. 



83 



cannot regard them as more than a variety in which the central convex part is 

 rather narrower and more elevated than usual (fig. 14). 



Remarks. — G. alxformis belongs to Freeh's 1 ' Group of Gervillia Hartmcuuti,' in 

 which the shell is obliquely rhombic and has numerous small teeth. 



Young specimens of G. al&formis differ from older examples in having well- 

 marked radial ribs, in the valves being less inflated, and in the occurrence of a 

 wing-like projection on the posterior ear. They resemble the form described by 

 d'Orbigny as Avicula Gottaldina, but in the latter the radial ornamentation and 

 well-marked posterior wing are retained in the adult state, whereas they soon 

 become obsolete in G. alasformis. I am not acquainted with the character of the 

 hinge of Avicula Gottaldina. 



Pig. 1 4.— Gervillia almformis (Sowerby). Lower Greensand (Perna-bed), Atherfield. Sedgwick Museum. 



Left valve of a narrow variety, x \ . 



Type. — The type cannot be found ; it came from the Lower Grecnsand (prob- 

 ably the Perna-bed) of Sandown, Isle of Wight. 



Distribution. — Perna-bed of Atherfield and Sandown. Crackers and Bed 1 1 

 (of Fitton) of Atherfield. Atherfield Clay of Haslemere. Hythe Beds of Hythe 

 and Lympne. 



Gervillia rostrata (Sowerby), L836. Plate XI, figs. 12a, 6, 13-23. 



1836. Pekna rostkata, J. de C. Sowerby. Trans. Greol. Soc, ser. "J, vol. iv., pp. 



241, 342, pi. xvii, fig. 17. 

 1846. Avicula cenomanensis. A. d'Orbigny. Pal. Franc. Terr. Crel., vol. iii, p. 



476, pi. cccxci, figs. 11—13. 

 1850. d'Orbigny. Prodr. de Pal., vol. ii, j>. 167. 



1 'Centralb. fur Mm., - etc. (1902), p. 613. 



