120 
148. Hotopra Errensis (Nicholson). 
(Plate II., Fig. 9). 
Shell turbinated, with a large ventricose body-whorl. Apical angle 90°. Volutions 
nearly four ; spire small, elevated; all the whorls convex, and the body-whorl very strongly 
rounded, and ventricose. Sutures deep. Aperture broad ovate, or sub-circular ; the outer 
lip bent inwards towards the base ; the peristome thick, and either entire or only confluent 
with the columella for a short distance. A minute umbilicus (?). Surface with no spiral 
band, but with revolving thread-like striz, about eight of them in the space of one line. No 
transverse striae. 
Height of specimen eight lines, of which the spire occupies less than two lines; width 
(including the aperture) ten lines. Height of aperture five lines ; width the same. 
This form is allied to Holopea Guelphensis and H. Gracia (Billings), but is a smaller form 
than either. I cannot identify it with any previously recorded form, and have therefore des- — 
cribed it as new. 
Locality and Formation.—Corniferous Limestone, Ridgeway. 
Genus HELICOTOMA (Salter). 
The name Helicotoma was proposed by Salter for a group of shells which he believed to 
form a sub-genus of Scalites, aud to be distinguished by their depressed discoid form, their 
nearly flat spire, the obtuse angulation of the whorls externally, their broad umbilicus, and 
their cirrhoid or helicoid form. In the typical species the umbilicus is wide, and the aper- 
ture is deeply notched above ; but the latter feature does not appear to be constant. So far 
ag is certainly known, the genus is exclusively Upper Cambrian and Lower Silurian. 
It is with extreme doubt that I refer any Devonian shell to this genus, but the Cornifer- 
ous Limestone has yielded casts of a shell which agrees in all respects with such a form of 
Helicotoma as H. cucharis (Billings), except in the small size of the umbilicus, and which I can 
not at present refer to any other recognised genus. In the meanwhile, therefore, I shall des- 
cribe the following species under Helicotoma, though it is exceedingly probable that better 
examples will show that this is not its true generic position. 
149. HELICOTOMA SEROTINA (Nicholson). 
(Plate II., Figs. 8, 8a). 
Shell small, of three or four volutions, which increase gradually in size to the aper- 
ture. Spire depressed, almost perfectly flat, the upper surface of the body-whorl lying on the 
same plane as the spire. Upper side of the body-whorl sloping slightly to the suture. All 
the whorls are angulated above, so that the shell slopes from the margin of the discoid upper 
surface all round to the centre of the base. Aperture large, sub-rhombic, the outer angle 
not notched (?), the inner angle prolonged much further inwards than the upper ; umbilicus 
small, with steep sides, not exposing the whorls within. 
Surface with numerous, close-set, revolving striz, and exhibiting (in the cast) no traces 
of a spiral band. 
Height six lines; width one inch; height of aperture six lines; from the inner to the 
outer angle eight lines ; width five lines. Diameter of umbilicus one line. 
I have been greatly puzzled where to lo- 
cate this singular fossil. But for the marked 
angularity of the whorls on their external 
and superior margin and the apparent com- 
plete absence of a band, I should certainly 
have considered the species as being a dis- 
coidal form of Plewrotomariu. As it is, the 
Z general form of the shell is singularly like 
Fig. 53. that of Helicutoma or Raphistoma, and it may 
a.Under surface of Helicotoma? serotina (Nich.), showing the be that it is to the latter of these types that 
cast, hors tee Conserede rine ee Prom’e natural lat, should he, referred, since, ita. mmapilons: fg 
very small. These, however, and all the 
