548 F. R. C. Reed — Woodwardian Mmeum Notes. 



some of the passage rock is merely a sheared felsite with secontlary 

 mica deposited on the shear-surfaces, the central part of the shear- 

 zone consists of true foliated schist. 



Dr. Irving seems to employ the tei"m " shenr-plane " in a sense 

 entirely different from my definition and description (1889, pp. 476, 

 477). My shear-planes do display a "rough parallelism," and 

 they do not "cut through the rock-mass at all angles to the quarry 

 face." Dr. Irving says that his "shear-planes" "are often con- 

 spicuously slickensided," and from his description of them, I should 

 be disposed to think that they are merely the effects of crushing 

 and sliding taking place long after the schist-making process was 

 completed. This sort of thing is well-known and well-understood, 

 and has no bearing upon the facts and theories set forth in my 

 papers. 



It should be clearly understood that it is impossible to see into 

 the mechanism of the schist-making process in the Malvern rocks 

 without the study of large numbers of microscopic slides. As Dr. 

 Irving has not given us any details of microscopic structure, we are 

 left in the dark as to the evidence on which he bases his conclusions. 



V. — On Yorkshire Thecidea. 

 By John Francis Walker, M.A., F.G.S., etc. 



I HAVE obtained a considerable number of specimens of Thecidium 

 ornatum, Moore, from the Coral Rag, in the bed containing 

 PhaximieUa (Pseudomelania) striata ; Psendodiadema versipora, 

 Uemieidaris intermedia, etc., from a quarry between Ayton and 

 Scarborough. My friend, the late Mr. Charles Moore, F.G.S., gaveme 

 some specimens of this Brachiopod from the Coral Rag of Lyneham, 

 Wiltshire, with which the Yorkshire Thecidium perfectly agrees in 

 form. This shell, especially the dorsal valve, is plentiful at Ayton, 

 but it is troublesome to find on account of its small size ; it is 

 best obtained by washing the marl ; occasionally it is found attached 

 to Ostrea. In my paper " On the Yorkshire Brachiopoda," York. 

 Phil. Society Report, 1888, I remarked that a species of Thecidium 

 occurs at Sufifield, near Scarborough, in the Lower coi'al rag, generally 

 attached to specimens of Zeilleria Hudlestoni. I have lately obtained 

 by washing the sand some perfect shells, and consider that they are 

 probably Thecidea Moreana, Buvignier. 



VI. — Woodwardian Museum Notes. 

 By F. R. CowPER Reed. 



AMONGST the Carboniferous Crinoidea in this Museum an 

 abnormal form of Platycrinus pileatus, Goldf., from the Car- 

 boniferous Limestone of Bolland was recently discovered by me 

 wliilst cataloguing the collection. This specimen has only four arms 

 and the calyx has suffered a corresponding diminution in the number 

 of its plates. The cup is conical, and when viewed from the base 

 roughly quadrangular : it expands somewhat rapidly so that its 

 greatest diameter is only sliglitly less than its height. The three 



