GERVILLIA. 



83 



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

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



Rcinarls. — G. al.'vforinu belongs to Freeh's ^ ' Group of GeroUlia ITarlmanni,' in 

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



Young specimens of G. alxformis 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 GottahUna, 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. ala'formis. I am not accjuainted with the character of the 

 hinge of Avicula Guttaldina. 



Fiu. 14.—GervilliaaLv/ormis (Soworhy). Lower Greoiisaiul (/'(.(•Ha-bed), Atherfield. Sedgwick Museum. 



Loft valve of a narrow varioty. x J. 



Ti/pr. — The type cannot be found ; it came from the Lower Greensand (prolj- 

 ably the Fenia-hed) of Sandown, Isle of Wight. 



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

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

 and Lympne. 



Gervilllv rosteat.v (Soicerbij), 1830. Plate XI, figs. 12 a, A, 13-23. 



183G. Peuna rosteata, /. de C. Sowerbij. Traus. Gool. Soc, scr. 2, vol. iv., pp. 



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

 1846. Avicula cenomanensis, A. d'Orbigny. Pal. Fran9. Terr. Orel., vol. iii, p. 



476, pi. cccxci, figs. 11—13. 

 1850. — — d'Orbigny. Prodr. de Pal., vol. ii, p. 167. 



1 'Ceutralb. fur Min.,' etx;. (1902), p. 613. 



