216 GASTEROPODA OF THE INFERIOR OOLITE. 
152. Nerinza (Ptygmatis) xenos, sp. nov. Plate XV, figs. 4 a, 4 b. 
Description : 
Spiral angle (regular) : : . a 
Height of whorl to width (approximate) af alseals 
Shell cylindrical, slightly turrited. Whorls tolerably numerous, for the most 
part flat, but slightly constricted about three-fourths of the way down. The 
suture is situated in the middle of a sutural belt of moderate prominence, 
which becomes almost effete in the later whorls. Sutural angle oblique. The 
ornaments consist of numerous fine spiral lines, of which one, rather larger than 
the rest, occupies the hollow of the constriction; they seem to fade away in the 
later whorls. 
The section shows five principal folds of a peculiar character. The anterior fold 
on the outer wall is much extended longitudinally ; it is broad-headed, and deve- 
lops slight subsidiary folds; the posterior fold is small and curved. Of the folds 
on the columellar side, the lowest is much extended longitudinally, the second is 
shght, the third (on the posterior wall) is narrow and deep. 
Relations and Distribution—The whorls are relatively higher than in Ptyq. 
pisolitica, and the peculiarly extended character of the lower folds of the section 
still further helps to differentiate it from that species, to which it is probably the 
most nearly allied. There seems also to be some slight differences of ornamen- 
tation, but the indications are obscure, even if they be of much specific value. 
Ptyg. wenos is interesting as occurring on the lowest horizon of any Nerinxa 
yet discovered in the Cotteswolds. It is met with somewhat sparingly in the 
shell-bed below the Lower Limestone on Crickley Hill, which is on the border-land 
between the Murchisonx- and the Opalinus-zone. Whether this species or Nerinxa 
cingenda is the oldest member of the genus in England remains yet to be deter- 
mined; if the Nerinxa-bed of the Dogger is strictly on the Pea-grit horizon, as 
supposed by some, we must regard Ptgy. wenos as the oldest Nerinea at present 
known in this country. 
The following group of species has this much in common, viz. that each 
possesses, or is presumed to possess, an internal structure very similar to that 
of Nerinxa Oppelensis, Lycett. The section has seven folds, but although the 
folds are so numerous, they do not seem to restrict the space so much as is 
the case in some other species of Ptygmatis presently to be described. This 
group appears to be represented in the Bathonian of France by Nerinxa 
bacillus, D’Orb. 
