196 GASTEROPODA OF THE INFERIOR OOLITE. 



fossils having been remaniS from earlier beds destroyed by contemporaneous 

 erosion. At Great Ponton only Nerinsea has been noticed by me ; the 

 specimens are less fragmentary than at Weldon, but their surface condition is 

 sadly apt to mislead. When to these difficulties we add the prevalence of dimor- 

 phism, it must be allowed that the Nerineeas of the upper beds of the Lincoln- 

 shire Limestone (Weldon and Great Ponton) constitute about as undesirable 

 a group as any one could have to investigate. One thing, I think, comes out 

 pretty clearly, viz. a strong admixture of forms related to and nearly identical 

 with those in Bathonian beds. 



Section A (Uniplioat^). 



121. NEEiNiiiA (Nerinella) gracilis, Lycett, 1857. Plate XII, figs. 12, 13 a, 13 h. 



1853. Chemnitzia gbacilis, Lyeett. Proc. Cottesw. Nat. Field Club, vol. i, p. 79, 



pi. ii, fig. 3. 

 1857. NEEiN.a;A geacilis, Lycett. Cotteswold Hills, p. 124, pi. ii, fig. 3. 

 1887. _ _ _ Witchell, Proc. Cottesw. Nat. Field Club, vol. 



ix, p. 37, pi. ii, fig. 2. 



Description : 



Spiral angle .... 5° — 8°. 



Height of whorl to width . . . 1 : 1'15. 



Approximate length . . . 60 — 140 mm. 



Shell cylindrical, scarcely turrited. Whorls twenty-five or more, with a slight 

 posterior prominence in the younger shells ; flat or very slightly turrited in the 

 more matured whorls. No sutural carina. Fine spiral lines mark the anterior 

 portion of each whorl, of which the prominent portion is smooth. In the more 

 advanced stage the whorls are smooth. 



Aperture ovate-oblong, with a narrow and but slightly twisted canal. Section 

 uniplicate, with one simple fold in the middle of the outer wall. 



Relations and Distribution. — In order not to multiply specific names unduly a 

 considerable breadth of variety as regards spiral angle has been admitted in this 

 case. It is just possible that fig. 12 may represent a narrow variety, of which 

 fragments representing very long shells are occasionally found. Lycett's type 

 was from the Oolite MarP horizon at Nailsworth Hill ; the other specimens are 

 from the Oolite Marl of Swift's Hill or Longridge, where N. gracilis is moderately 

 plentiful in fragments. In the Lincolnshire Limestone, specimens of Nerinella not 



1 In referring to the Oolite Marl the horizon is meant, see p. 61, antea. 



