i66 



PROCEEDINGS OF THE GEOLOGICAL SOCIETY. 



3 : other genera (Avieula, Area, &c.) only one or two species 

 each. 



In South Wales 11 genera and 26 species have been collected. 

 The genera are the same, but with specific additions to Modiolopsis 

 and Mytilus. 



Of the 3 Irish genera the 6 species are — Pterincea lineata, 

 Goldf., P. planulata, Conr., and P. retroflexa, WahL, Cardiola 

 fibrosa, Sow., and C. interrupta, Brod., with Goniopliora cymbceformis, 

 Sow. ; none are confined to the Irish beds. Only 5 genera and 8 

 species of Lamellibranchiata are really peculiar to the Wenlock 

 series. 7 genera and 15 species came in from the Upper Llandovery ; 

 3 of these 15 are Lower Llandovery also, viz. Pterincea retrofiexa, 

 Cardiola interrupta, and Mytilus mytilimeris ; 2 of the same are 

 Caradoc, and 3 species came direct from the Caradoc ; they are 

 Pterincea tenuistnata, M ; Coy, Area (Pcdcearca) edmondiiformis, 

 !M*Coy, and Ctenodonta anglica, D'Orb. Thus the Wenlock is united 

 to the Upper Llandovery below through 17 species, and to the Lower 

 Ludlow above by 21 species, and these all pass to the Upper Ludlow, 

 so that the actual number of peculiar Lamellibranchs, or the 

 Bivalve fauna, is reduced to the following 8 species : — Ambonycliia 

 tumida, Sollas, Pterincea asperula, M'Coy, and P. laminosa, Goldf., 

 Chidophorus planulatus, Conr., Modiolopsis acutipora, Sollas, M. 

 inflata, var., and M. cliemungensis'l , Conr., with Mytilus unguicu- 

 latus, Salt. Nevertheless, assuming that the transgressional species 

 also strictly belong to the rocks in which they occur, the Wenlock 

 Bivalve fauna consists of 25 species by retaining those forms that 

 pass up to the Ludlow. 



Gasteropoda. — Looking at the splendid Ccelenterate, Echino- 

 dermal, Crustacean, and Brachiopodal faunas in the Wenlock series, 

 the distribution and ranges of which we have analyzed and tabu- 

 lated, we should have expected this class to have been more 

 largely represented, especially as during the Caradoc and Upper 

 Llandovery periods a larger molluscan fauna existed, although 

 apparently the nature of the sea-bed was not so favourable as that 

 of the more calcareous and argillaceous condition of the Upper 

 Wenlock, in which the great mass of the Wenlock fauna occurs. 

 All the genera belong to the order Prosobranchiata and division 

 Holostomata. The Caradoc Gasteropoda, as we have seen, number 

 11 genera and 53 species, the Wenlock 9 genera and 27 species ; 

 the 9 genera represent 5 families. One species only occurs in the 

 Tarannon Shale (Acroculia haliotis), and ranges through to the 

 Wenlock Limestone and Ludlow. The Denbighshire Grits contain 

 Acroculia haliotis, Holopella graeilior, Loxonema elegans, Murchi- 

 sonia articvlata, and M. Lloydi, or 4 genera and 5 species. The 

 Woolhope exhibits but a small fauna, only 8 species, 4 of which are 

 Euomphali and 2 Acroeulice, with Trochus (Cydonema) eccaltatus and 

 Turbo tritorquatus. In this, as in all the other classes, nearly every 

 species known occurs in the Upper Wenlock ; thus the 9 known 

 genera and 24 out of the 27 species belong to that horizon. 7 genera 

 and 17 species occur in South Wales, but only 1 in Scotland 



