216 SUPPLEMENT TO THE 



internal cast, of which I have figured and briefly described for the sake of facilitating 

 comparison.^ 



I have named this large and fine Lower-Silurian Crania after its discoverer, C. Croft, 

 Esq., of Manchester, who kindly sent me his specimens for description and illustration. 



Genus — Pholidops, Hall, 1859. 



157. Pholidops implicata, Salter sp. Dav., Sil. Mon., PI. VIII, figs. 13—18; Sil. 



Sup., PI. XVII, fig. 48. 



This small species is fully described at p. 80 of my ' Silurian Monograph ' as Crania 

 implicata, Sow. sp. Since then I have considered it desirable to retain for it Hall's 

 generic name " Pholidops." Although closely related to Crania it differs from it in some 

 particulars, both valves being free. It is not a very rare Wenlock fossil. Mr. G. Maw 

 obtained it through his washing operations in the Upper and Lower Ludlow, and in shales 

 above the Wenlock Limestone in the neighbourhood of Benthall Edge and Bromley, more 

 abundant in the Upper Wenlock Shales or Tickwood beds, near Tickwood, Salop ; also, 

 but less abundantly, in the Lower Wenlock Shales at Buildwas in the same county. It 

 is also found in the Wenlock Limestone. In Scotland it occurs in the Wenlock series of 

 the Pentland Hills, and Mrs. R. Gray has obtained it from the Middle Llandovery at 

 Woodland Point as well as from the Penkill beds at Penwhapple Glen in Ayrshire. It 

 has also been collected by Prof. Lindstrom in the Wenlock rocks of the Isle of Gothland. 



1 Ceania Rycholtiana, c?e ^owmcA. Dav. Carb. Monograph, pi. xlviii, figs. 15, 16, 17, and Sil. 



Sup., pi. XVII, fig. 57. 



I have already described this fine species at p. 195 of my 'Carboniferous Monograph,' and have given 

 figures of its exterior. Since then Mr. W. H. Baily, of the ' Geological Survey of Ireland,' found a large 

 and very fine internal cast of the upper valve of this species in the Lower Carboniferous Limestone at 

 Townland of Legilly, near Castlecaulfield, County Tyrone, Ireland, among the debris of an old quarry. 

 The specimen belongs to the Museum of the Geological Survey of Ireland; it measures \A\ lines in 

 length by 15 in breadth and 5 in depth, and is almost circular and conical, with the apex at about 

 the centre. The muscular and vascular impressions are clearly defined. The specimen is much less deep 

 or conical than is the Crania Crofti, and does not possess the anterior sinus or depression characteristic 

 of the Lower-Silurian form. 



