498 Dr. John Lycett — Note on Purpuroid Shells. 



latter is much the closer. The green chlorite schists, whicli are so 

 marked a feature in Anglesey, are almost equally conspicuous in the 

 Carnsore area; while the gneissose and granitoid types are also 

 similar in both localities. In Anglesey, however, granitoid rock 

 forms a thick band at the summit of the series, while, in Wexford, 

 granitoid seams, usually of no great thickness, are intercalated with 

 the green schists. It is also to be observed that if the strike of the 

 Anglesey schist were produced to the south-west, it would pass 

 through the Carnsore district. The massive, highly crystalline 

 character of the Lewisian gneiss, together with the predominance of 

 hornblendic and micaceous constituents, strongly distinguishes it 

 from the Carnsore schists. 



These four types, Ordovician, Cambrian, Pebidian, and (?) Dimetian, 

 are represented in this narrow band. All the groups have a pre- 

 vailing strike to the west-south-west, but wherever observed, and 

 sections described as critical were selected, there were no indications 

 of a passage between any two of the formations. 



I have recognized the Pebidians in other parts of Leinster, but 

 their description lies beyond the scope of the present paper. It 

 may perhaps be hoped that the discovery of this new series in 

 Ireland will clear up some difficulties. The lithology of these rocks 

 has obviously perplexed Irish geologists, and they have been referred 

 to more than one formation. Their distinct mineral chai'acters 

 should, however, enable their distribution to be determined. 



I had not intended to publish anything on Irish Archaean geology 

 until I had visited other districts, but Mr. Kinahan's challenge 

 seemed to call for reply, and I have ventured to contribute from my 

 notes such facts as bear upon his views. 



VII. — Note on the Generic Distinctness of Puupuroidea and 

 Purpura, with Kemarks upon the PuRprROiD Shells figured 

 IN THE Geol. Mag. Plate YIII. Decade II. Vol. VIL 1880. 

 By John Lycett, L.R.C.P.E., and M.E.C.S. Engl. 



THE genus Piirpuroidea was described by me in 1848 from three 

 species in the Great Oolite of Gloucestershire, and published 

 in the Annals and Magazine of Natural History, accompanied by 

 woodcuts representing one of the species. Before that period M. 

 Buvignier had described and figured three species of the same 

 genus from the Coral Rag of France, Mem. Soc. Philomath. Verdun, 

 1843, accompanied by plates illustrating the species, which he 

 assigned to the genus Purpura ; these figures were for the most 

 part insufficient for the purposes of generic discrimination, and 

 founded upon specimens more or less imperfect ; one of them was 

 believed by me to be identical with the species figured in my 

 woodcut, and was accordingly named by me Purpuroidea nodidata, 

 the name of the species having been adopted from the Murex 

 nodulatns of Young and Bird, which was also believed to be identical 

 with the Gloucestershire species. At the period in question (1848) 

 only one other Jurassic species attributed to the genus was known, 

 viz. the Murex tuberosus of Sowerby's Mineral Conchology, tab. 578, 



