76 Geological Society. 



other merely a sinus. As the outer lip is rarely well preserved, it 

 is difficult and sometimes impossible to decide whether a particular 

 individual belongs to one or other of these two types. With 

 regard to these shells, two important questions require to be 

 answered. Firstly, whether the slit or the sinus characterizes the 

 more primitive type ; and, secondly, whether the elongated Mur- 

 chisonia and the shorter Pleurotomaria are both derived from the 

 same stock, and which of them appears the earlier. Before con- 

 sidering the British evidence, the work of foreign palteontologists is 

 reviewed by the authoress. From the material at present available, 

 in the British Isles as well as in America and the Baltic Provinces, 

 elongated forms with a sinus precede those with a slit. There are 

 at least two distinct groups of sinuated shells with a band : one, 

 containing Hormoioma, Ectomaria, etc., having the lines of growth 

 sweeping back to and forward from the band very obliquely; and a 

 second, containing Loj^ihospira, having the lines less oblique and 

 agreeing more in direction with those of Murcliisonia, only the band 

 is prominent instead of being grooved. A possible third group is 

 indicated by a subgenus, subsequently described, in which the lines 

 of growth are but slightly oblique and the band grooved. The 

 first two groups in Britain range from Upper Cambrian to Silurian 

 rocks, and the third from the Bala to the Silurian. The genus 

 Mu.rchisonia may have begun in the Wenlock Formation. So far, 

 no light is thrown on the question as to whether Murchisonia and 

 Fhuroiomaria were derived from the same stock, nor has the 

 authoress yet met with any specimens showing a transition from 

 sinus to slit. 



In the latter part of the paper three new subgenera, eleven 

 new species, and one new variety are described and figured. 



April 30th, 1902.— Prof. Charles Lapworth, LL.D., F.R.S., 

 President, in the Chair. 



The following communication was read : — 



' Revision of the Phyllocarida from the Chemung and Waverly 

 Groups of Pennsylvania.' By Prof. Charles Emerson Beecher, Ph.D., 

 F.C.G.S. 



The specimens described in the paper, as well as those on which 

 the original descriptions were based, were all obtained in the vicinity 

 of Warren, Philadelphia. The chief horizon is in the shale-beds of 

 the Upper Chemung Group, about 50 feet above mean water-level 

 in the Allegheny Eiver. The deposits are called by the writer the 

 ' Phyllocarid-Beds.' Additions and emendations to the original 

 diagnoses of the following genera and species are given : — Echino- 

 caris sociaUs, Beecher ; Tro^ndocaris, Tr. hicarinata, Beecher, Tr. 

 alternata, Beecher ; Ely mo carls, E. sUiqua, Beecher ; and two new 

 species of Echinocaris are described. 



