GASTEROPODA. 73 



Crossostoma? discoideum. Plate XI, figs. 7, la, lb. 



C. Testa Icevi, depressd; spird prominuld; anfractibus angustatis, suturis impressis; 

 aperturd parvd, suborbiculari. 



Shell smooth, depressed ; spire but little elevated, or nearly flat ; whorls narrow, the 

 sutures distinct ; aperture small, basal nearly round. The height is equal to half the basal 

 diameter. 



This is, probably, only a variety of C. Prattii, and in a state in which all our Great 

 Oolite specimens occur — the outer lip not being quite entire, and extremely thin and 

 slightly rugged, never perfecting a well-defined lip (C. discoideum) ; the change to the 

 ultimate condition occupies a space which does not exceed one fourth of a volution, a 

 few rugged lines of growth are formed; an irregular lamina next protrudes, forming a kind 

 of frill around a contracted, thickened, and orbicular aperture, as in C. Prattii. 



Locality. Minchinhampton Common and Bussage, at which places it occurs somewhat 

 rarely, and in more than one of the shelly beds. 



Crossostoma? helictforme. Plate XI, fig. 8. 



C. Testa Icevi, turbinatd, subdepressd; spird parvd prominuld; anfractibus convexi- 

 usculis; aperturd ellipticd. 



Shell smooth, turbinated, somewhat depressed ; spire small, but little elevated ; whorls 

 rather convex ; aperture elliptical. 



Locality. It is somewhat rare ; our specimens have been obtained from the planking 

 of Minchinhampton Common ; it is likewise found in the middle division of the Inferior 

 Oolite at Leckhampton, near Cheltenham. 



This species has the general form of C. discoideum, but the spire is more elevated ; 

 they are only provisionally referred to Crossostoma, having somewhat the aspect of Mono- 

 donta, and even (in C. discoideum), the thickened base of Rotella. 



Phasianella, Lam. 1812. 



Shell oval, smooth ; aperture oval, entire, forming an acute angle posteriorly at the 

 junction of the columella and outer lip ; outer lip thin ; inner lip spread over a portion of 

 the columella. 



The Great Oolite shells provisionally referred to this genus are small, and like their 

 recent congeners, individuals of the same species offer a considerable variety of form, which 

 makes their determination rather difficult. 



