THE 



GEOLOGICAL MAGAZINE 



NEW SERIES. DECADE IV. VOL. I. 



No. VI.— JUNE, 1894. 



0:RXG-XlSTJi^JL. JLI^TICLES. 



mi 



I. WOODWAKDIAN MuSEUM NOTES. 



By F, E. CowPER Eeed, B.A., F.G.S. 

 (PLATE VII.) 



IHE sub-genus Ghasmops of the genus Phacops is so rarely, if 

 JL ever, found in great Britain, except as disconnected heads and 

 pygidia, that a specimen which shows the cephalic shield attached to 

 several thoracic rings deserves notice. 



The two British species recognised by Salter (omitting the doubt- 

 ful Ch. Julcesii) are Ch. macroura (Sjogren) and Ch. conophthalmus 

 (Boeck?),' but he apparently perceived that more than two species 

 were included under these names (Mon. Brit. Tril. p. 38). The 

 material in Britain available at that time, however, was not well 

 enough preserved, and the investigation of the Continental forms 

 of this characteristically North-European group was not sufficiently 

 advanced to admit of a more complete discrimination. But now Fr. 

 Schmidt's work on the Silurian trilobites of the East Baltic provinces 

 (Mem. TAcad. Imp. d. Sc. d. St. Petersb. vii. ser. T. xxx. No. 1) has 

 supplied a long-felt want, and we can only regret that the British 

 specimens of Chasmops generally occur in such an unsatisfactory and 

 fragmentary condition as to preclude their indentification or com- 

 parison with those he has so fully described. The material with 

 which he has had to deal is in a comparatively excellent state of 

 preservation, and it is gratifying to find an English specimen which 

 does not unfavourably compare with some of his. Such is the case 

 with the one now described. It was discovered by Mr. F. Marr in 

 the Coniston Limestone of Applethwaite Common near Windermere. 



The head and 7-8 thoracic rings are preserved, but they have 

 suffered considerable lateral compression, producing irregular cracks 

 and corrugations of the surface together with some distortion. 

 For instance, the parabolic shape of the cephalic shield is mis- 

 leading, for probably it was originally semicircular and the 

 proportion of the length to the breadth about 1:2. In the thorax 

 the axis has been squeezed into greater prominence, and on the 

 pleurae antero-posterior wrinkles have been developed. The actual 

 measurements of the specimen in its present state are as follows :— 



* According to Fr. Schmidt, Salter's species are not those of Sjogren and Boeck. 



DECADE IV. VOL. I. NO. VI. 16 



