120 



148. HOLOPEA ERIENSIS (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 striae, 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. Gratia (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, and 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 

 as 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 &sH eucharis (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 strise, 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 Pleurotomaria. As it is, the 

 7 general form of the shell is singularly like 



Fig. 53. that of Helicotoma or Raphistoma, and it may 



a. Under surface of Helicotoma'! serotina(ffich.), showing the be that it IS to the latter of these types that 

 minute umbilicus ; 6. Front view of the same. From a natural : f iij u rp f prrp J ,: npp ,> nmhilimis ii 

 cast from the Cornifereus Limestone. ' a > slnce 



very small. These, however, and all the 



