314 MISS DONALD ON PROTEROZOIC GAsTEROPODA | May igo2, 
evolved from the other? Secondly: are the elongated Murchisonia 
and the shorter Pleurotomaria both derived from the same stock, and 
which appears earlier? We need also to know the full value of the 
presence or absence of a sinus or slit in classification, and what 
special characteristics are associated with each respectively. 
Before considering the British evidence on these points, it may 
be well to review the results of the investigations of some foreign 
paleontologists. Messrs. Ulrich & Scofield and Prof. Koken have | 
devoted considerable attention to the study of the origin of these 
shells, and the former also to these differences in structure. 
The researches of Ulrich & Scofield icad them to the conclusion 
that the sinus is older than the slit, and they regard Raphistomina, 
Ulr.,’ as the most primitive genus of this group, it being represented 
by Pleurotomaria laurentina, Billings, in the Calciferous Series. 
They place this genus in the family Raphistomide, and unite it with 
the Pleurotomariide, Euomphalide, and Trochide in a new suborder, 
which they name Eotomacea. They consider that this suborder 
should moreover include the Fissurellide, Haliotide, Turbinide; 
and provisionally also the Maclureide, because of their evident 
relations to the Euomphalide. The Raphistomide are characterized 
by a short form, and have in the outer lip a sinus only, which does not 
give rise to a band on the whorls. The family contains shells which 
these authors regard as ‘the best known representatives of the original 
stock from which’ the other families ‘were almost simultaneously 
evolved.’ They are acquainted with only two Lower Silurian 
(Ordovician) species possessing a deep parallel-edged slit, namely : ~ 
Schizolopha teaxtilis, Ulr., from the upper part of the Trenton Group, 
and Sch. Moorei, Ulr., from the Lorraine and Richmond Groups, 
both of which are short forms. The depth of the slit in the 
former is about two-ninths of the circumference of the last whorl ; 
in the latter it is about one-fifth. Schizolopha, Ulr., is referred to 
the Pleurotomariide, in which family Ulrich & Scofield include all 
genera, whether elongated or short, that possess either a sinus or a 
slit in the outer lip, giving rise to a band on all the whorls. Thus they 
place here such elongated forms as Hormotoma, Celocaulus, Turri- 
toma, and Solenospira, Ulr. (Ectomaria, Koken), which other writers 
have regarded as closely allied to MWurchisonia, though they have 
not a slit, but a sinus. They state*® that none of these genera 
can be properly united with Murchisonia, and they are doubtful 
whether MW. coronata, Goldf., the type-form of Murchisonia, is a true 
member of the Pleurotomariide. 
Prof. Koken diverges somewhat from Ulrich & Scofield in his 
grouping of the genera. In 1896,* previous to the publication of 
the work on Minnesota, he proposed a new suborder, which he 
called Sinuata; in this he placed the Raphistomide, Kuompha- 
lide, Euomphalopteride, Pleurotomariide, Haliotide, Fissurellide, 
| Final Rep. Geol. & Nat. Hist. Surv. Minnesota, vol. iii, pt. ii (1897) p. 948. 
2 Ibid. p. 9380. 3 Ibid. pp. 959-60. 
* Jahrb. d. k.-k. geol. Reichsanst. vol. xlvi, p. 61. 
