xlviii ADDENDA. 
are here reproduced by the kindness of the Editor of the Geological Magazine. The Ateleocystites Husleyi, 
Billings (Canadian Fossils, Dee. 11. p. 73), with which the above species has been compared, is smaller and 
less broad, and was obtained from the Trenton limestone. The A. cornutus, Hall, 1. ¢, p. 133, Plate 7 A, 
figs. 5—7 is from the Pentamerus limestone of the Lower Helderberg group, and the A. disparilis, Hall, le. 
p. 145, Pl. 88, figs. 1—4 is from the Oriskany sandstone. Another form referred to this genus from the 
Upper Caradoc of Shole’s Hook, Pembrokeshire, is in the collection of the Geological Survey. 
Tremadoe Group, p. 15:—In a paper read before the British Association (Aug., 1872), Dr Hicks fully 
confirmed the occurrence of the Tremadoc rocks previously recognised in 1866, by Mr Salter and himself at 
Ramsey Island, St David’s, where they overlie the Lingula flags, and are from 800 to 1000 feet in thick- 
ness, with numerous fossils, nearly all the species as well as many of the genera being new. They com- 
prise Brachiopoda of the genera Lingula, Orthis, Obolella, and the Lamellibranchiate genus Ctenodonta, also 
species of Orthoceras, Theca, Bellerophon, an Encrinite and a Starfish, besides nine species of Trilo- 
bites belonging to Niobe, Conocoryphe, Cheirurus, and a genus allied to Dikellocephalus. These are followed 
by the Arenig group having a thickness of a 1000 feet, and contain the genera Asaphus, Ogygia, dglina, 
Trinucleus, Ampyx, Calymene and Agnostus; also Conularia, Theca, Orthoceras, Bellerophon, Lingula, Orthas. 
In this group Mr J. Hopkinson has recognised more than 20 species of Graptolites, belongimg to the genera,— 
Didymograpsus, Tetragrapsus, Phyllograptus, Ptilograpsus, Dendrograpsus, Callograptus, Retiolites and Logano- 
graptus, and also Dictyonema, from which association Mr Hopkinson considers the beds to be the equivalent 
of the Quebec group of Canada, the Skiddaw slates of Cumberland, and the Arenig rocks of Shelve. 

