﻿Vol. 66.] THE ORDOVICEAN OF THE GLENSAUL DISTRICT. 279 



Plate XXII. 



Pig. 1. Xileus armadillo, Dalinan. Middle shield. X 2. Locality 62. 

 la. Do. Pygidium, internal cast. X 2. Locality 361. 



2 b. Do. Pygidium, interior of the test of the same specimen. X 2. 



3 a. Xiobe sp. Imperfect pygidium. X 2. Locality 155. 



3 b. Do. Interior of the test of the same specimen. X 2. 



4 a. Encrinurus octocostatus, sp. nov. Pygidium. X 3. Locality 62. 

 4 b. Do. Side view of the same specimen. X 3. 



5. Pliomera pseudoarticulata (Portlock). Middle shield. X 2. 



Locality 62. 



6. Do. Young individual, from Shangort. X 2. 



Discussion. 



The President remarked that there seemed nothing improbable 

 in the supposed inclusion of fragments of contemporary limestone 

 in the volcanic breccias. The tuffs which were deposited in the 

 formation of Monte Nuovo contained shells and fragments from 

 the adjacent sea-bottom, and recent formations of calcareous sand 

 Avere involved in the volcanic ejectamenta of Anchor Head, Hawaii. 



Mr. H. H. Thomas congratulated the Authors on a piece of work 

 which would prove of considerable interest to students of British 

 stratigraphy. He was relieved to find that the Tourmakeady and 

 Shangort Beds had been removed from the Llandeilo Series, and 

 placed in the Arenig : for, not only was the Didymograptus - 

 ecctensus Zone a horizon of widespread volcanic activity in the 

 neighbouring country of Wales, but the fauna of the Tourmakeady 

 and Shangort Beds had little in common with that of the calcareous 

 beds of the Welsh Llandeilo. It was, therefore, much more satis- 

 factory to find that this highly interesting fauna was not an 

 anomalous fauna of Llandeilo age, but dependent on a calcareous 

 facies of the extensus beds, which in South Wales are wholly argilla- 

 ceous and arenaceous. 



The speaker regretted that ' dependent ' graptolites allied to 

 Didymograptus bifidus were found associated with the zone- form 

 of D. extensus : for the separation of the Tetragraptus Beds from 

 the Llanvirn Series of Hicks, always a task of some difficulty, 

 would now be far from easy, unless fossils and exposures were 

 exceedingly numerous. It was fortunate, however, that in South 

 Wales ' dependent' species of Didymograptus were restricted to the 

 Llanvirn Series, and that D. extensus was confined to its own zone. 



With reference to the intrusive felsite, he asked whether the 

 Authors held any views as to the original nature of the rhombic 

 pyroxene which was represented by pseudomorphs ; also whether 

 there Avere any felspar phenocrysts, and whether it had been possible 

 to determine to what species they belonged. 



Mr. G. W. Young remarked that, in the uppermost section 

 exhibited, the felsite mass formed a prominent hill, while in the 

 bottom section, taken about a mile away, it occupied the floor of a 

 ■deep valley. He asked for an explanation. 



Prof. E. W. Skeats said that, while unfamiliar with the area 



