218 GASTEROPODA. OF THE INFERIOR OOLITE. 
length of the whorls, and by the absence of dimorphism; and from Ptyg. Jonesit 
by the absence of dimorphism and the more regular excavations of the whorls. 
A variety, which may be known as “ Carnicotensis” (figs. 5a and 5), 
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 Nerinza-bed at Little Ponton (fig. 6a), 
at Weldon (fig. 6), and in the highest part of the Freestone Series at Crickley 
(fig. 6c). This may be known as var. “cervicula.” There is a third variety 
(fig. 7a), which I would 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. bacillus and Ptyg. Oppelensis. 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-grit. The case is exceptional, as there are but few species of Nerinza 
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. 
bacillus, I would propose for it the name of Ptygmatis cervicula, the two other 
names to stand as varieties. 
154. Nermnaa (Ptygmatis) Jonusu, Lycett, 1857. Plate XV, figs. 9 a—e. 
1857. Nertyma Jonesu, Lycett. Cotteswold Hills, p. 124, pl. ij, fig. 4. 
1887. — — — Witchell, vol. cit., p. 25. 
Bibliography, Sc.—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 Bibel bee 
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. 
