Revieics — R. Etheridge' s Manual of Geology. 565 



'■' PoLYZOA. — Dictyonema sociale as in the Upper Lingula Flags, 

 also near Tremadoc in the passage-beds. 



" Bkachiopoda. — The Lower Tremafloc Brachiopoda are .... 

 Four of these genera and 6 of the 11 species pass to the Upper 

 Tremadoc 



" Pelecypoda (Lamellibranchiata). — The Tremadoc rocks of 

 Eamsey Island have yielded the first evidence of Pelec3'pod or 

 bivalve molluscan life in Britain. They are referable to 5 genera 

 and 12 species — Davidia (2), Glyptarca (2), Modiolopsis (4), 

 Palcearca (2), and Ctenodonta (2); none of the species are known 

 out of ... . the Lower Tremadoc. 



" Gasteropoda. — None known below the Arenig rocks. 



" Pteropoda. — The genus Theca is represented by five species in 



the Lower Tremadoc The three first named pass to the 



Upper Tremadoc 



" Heteropoda. — BelleropJion ramsayensis and B. solvensis charac- 

 terize the Tremanhire or Solva and Eamsay Island beds. 



" Cephalopoda. None below the Upper Tremadoc." 



Eeferring to the Hydrozoa, there appears to be a slight slip on 

 p. 58, where the author says, " No Ehabdophora are known below 

 the Arenig rocks," and also at p. 59, where he says, "No Ehabdophora 

 occur below this line anywhere." It is true that in both these cases 

 he is alluding to Wales, but it would have been safer to have made 

 a reservation. Again, in the general table, page 141, he quotes 

 Diplograptus pristis and D. folium as occurring in "Tremadoc Slates." 



The second section of the Lower Palteozoic rocks comprises 

 the Arenig or Skiddaw series ; the Lower Bala and Llandeilo 

 Flags ; the Caradoc Sandstone, Bala Beds and Coniston Limestone ; 

 and lastly the Lower Llandovery rocks. This grouping corresponds 

 in the main with the second fauna of Barrande, and comprises the 

 principal portion of the Lower Silurian of the Geological Survey. 

 The author has largel}'^ availed himself of the discoveries of Harkness, 

 Nicholson, Hicks, Lapworth and Callaway, whose labours, since the 

 first appearance of Phillips's Manual, have shed such a flood of light 

 on the palasontology of these at that time little known rocks. It is 

 quite within the memory of many of us that the Skiddaw rocks were 

 supposed to contain hardly any fossils : yet here we find 70 species 

 enumerated, mostly Graptolites. There may be some numerical 

 eiTor here, however ; for at p. 63 he says that 28 species of Ehabdo- 

 phora occur in the Skiddaw Group, whilst in Table VIII. p. QQ, there 

 are 48 species of Hydrozoa enumerated from Skiddaw, which is in 

 Cumberland, and not in Westmoreland, as the author supposes. In the 

 corresponding Arenigs of South Wales, out of 88 species enumerated, 

 the Hydrozoa and Crustacea are about equally represented. 



Certain authorities object to the per-centage system, which is no 

 doubt somewhat inelastic, and was perhaps more calculated to 

 command attention in the days when people attached greater 

 importance to " species " than is now the case. We know for 

 instance that Mr. Marr demurs to the system as one which in the 

 present state of synonymy and incomplete determination of forms 



