ANNIVERSARY ADDRESS OF THE PRESIDENT. 



121 



rocks, viz. 16 species of Hydrozoa, 17 Crustacea, and 23 Brachio- 

 pcda, or, together, 56 out of the whole 76 that connect the two 

 formations. It is interesting to know also those areas that are spe- 

 cifically most prolific in the above groups, and thus help us to draw 

 conclusions as to the nature of the sea and its bathymetrical condition 

 during the time of the deposition of the Llandeilo and succeeding 

 Caradoc, which are more intimately related than is generally believed. 

 United, the Llandeilo fauna of North and South Wales is constituted 

 by 94 species ; or this is the known number for Wales, 88 occurring 

 in South and 47 in North Wales, and 41 being common to both, 

 chiefly among the Hydrozoa and Crustacea. Upon whatever hypothesis 

 we may account for the physical relationship between the Llandeilo 

 rocks of Scotland and Ireland, the connecting species are few (only 

 27) ; and no Crustacea are common to these two countries — which, 

 out of a total fauna of 45 species, is remarkable. The Irish species 

 number 6, 3 of which are also South -Wales forms — Ogygia Port- 

 lockii, Calymene duplicata, and JEglina mirabilis. As before stated, 

 Scotland has hitherto yielded only 4 genera and 5 species of Crus- 

 tacea — Ulcenus Bowmanii, Salteria involnta, JS.primceva, Peltocaris 

 aptycJioides, and Discinocaris Browniana. 

 Plasty. — None. 



Protozoa. — Ischadites antiquus, Salt. No other Protozoon has 

 been recognized in the Llandeilo ; it is not a common genus in the 

 Lower Silurian rocks. 



Hydrozoa. — The Llandeilo beds of Scotland appear to be the most 

 prolific in Bhabdophora. Our knowledge of them is due to the 

 researches of Nicholson, Lapworth, and Carruthers in Scotland, all 

 of whom have done able work in elucidating the history and struc- 

 ture of this obscure class. Forty-four species illustrate 18 genera ; 

 but it is chiefly through the larger genera that this Graptolitic fauna 

 is represented. South Wales, as we should expect, is also represen- 

 tative, although poor, as compared with Scotland, having only 18 

 species, or about half the number. North Wales has 7 species, and 

 Ireland 28. The Welsh and Irish genera have not the same specific 

 value ; generally they are much the same, but illustrated by fewer 

 species. This may be due to want of systematic search in Wales, 

 such as the rocks of Scotland have undergone by the above-men- 

 tioned authors. The genera Didymograptus, Diplograptus, Clirriaco- 

 graptus, and Dicellograptus are those chiefly occurring in South 

 Wales ; and Diplograptus, Dicellograptus, and Climacograptus in 

 North Wales, &c. The Llandeilo rocks of Ireland contain species 

 of nearly all the above genera. Thus of the 44 known Llandeilo 

 Ehabdophora we have 



South Wales. 

 North Wales 

 Scotland . . . 

 Ireland 



Species. 

 . 18 



82 

 28 



85 occurrences ; 



and 16 species pass to the succeeding Caradoc. 



