218 GASTEROPODA OF THE IiNFERIOR OOLITE. 



length of the whorls, and by the absence of dimorphism ; and from Ptyg. Jonesii 

 by the absence of dimorphism and the more regular excavations of the whorls. 



A variety, which may be known as " Carnicotensis " (figs. 5 a and 5 b), 

 represents in part the earlier stages of the species. This form is not uncommon 

 in the Clypeus-grit horizon of the neighbourhood of Radstock. A very 

 cylindrical variety occurs in the upper Nerinsea-bed at Little Ponton (fig. 6 a), 

 at Weldon (fig. 6 h), and in the highest part of the Freestone Series at Crickley 

 (fig. 6 c). This may be known as var. " cerviculay There is a third variety 

 (fig. 7a), which I Avould describe as var. " crassicincta" from the great thickness 

 of the sutural belt ; the whorls also are not quite so high. This occurs in the 

 Pea-grit of Nailsworth Hill. The section is somewhat obscure, but is evidently on 

 the same plan as in Ptyg. hacillus and Ptyg. Op'pelensis. This form may ultimately 

 prove to be worthy of stronger distinction. But, accepting it as a representative 

 of the species now under description, we obtain a wide range from the Pea-grit to 

 the Clypeus-gvit. The case is exceptional, as there are but few species of Neringea 

 which can be regarded as common to the upper and lower divisions of our Inferior 

 Oolite. If I have been mistaken in referring our Inferior Oolite species to Ptyg. 

 hacillus, I would propose for it the name of Ptygmatis cervicula, the two other 

 names to stand as varieties. 



154. Nerin/ea {Ptygmatis) Jonesii, Lycett, 1857. Plate XV, figs. 9 a — c. 



1857. Nebinjea Jonesii, Lycett. Cotteswold Hills, p. 124, pi. ii, fig. 4. 

 1887. — — — Witchell, vol. cit., p. 25. 



Bibliography, ^'c. — Owing to the interior of the type specimen being filled 

 with spar, there is no chance of getting a section. Hence Witchell (op. cit., 

 p. 25) places N. Jonesii in the unclassified group. There can be little doubt that 

 it is a true Ptygmatis, though its excessive dimorphism causes the fragments 

 to be difficult of identification, as the two parts seldom occur on the same 

 specimen. 



Description : 



Spiral angle (approximate) . . . 4° — 5° 



Height of whorl to width nearly as . .1:1. 



Approximate length . . . .150 mm. 



Shell cylindrical, elongated, very dimorphous. Whorls about as high as wide. 

 The posterior whorls are excavated and much thickened posteriorly, so as to form 

 a strong sutural belt. The salience of this belt diminishes, the elevation of 

 the whorls becomes less, and ultimately the whorls become quite flat and without 

 any marked sutural prominence. 



