154 SUPPLEMENT TO THE 



39. Rhynchonella Lapworthi, Bav. Sil. Mon,, PI. X, fig. 7. 



Shell triangular, broadest and rounded anteriorly, tapering posteriorly, slightly wider 

 than long ; ventral valve moderately convex, with a wide, shallow sinus ; beak incurved, 

 flattened laterally ; dorsal valve rather more convex than the ventral one, slightly flattened 

 along the middle, posterior margins bent inwards, somewhat abruptly on each side of the 

 umbo; fold very slightly defined. Surface of valves ornamented with about fourteen 

 strong angular ribs, of which four or five compose the fold, three or four the sinus. 

 Length 6, width 7, depth 5 lines. 



Ohs. — Of this species Mrs. R. Gray collected six specimens of about the same size 

 and character from the Upper Llandeilo Limestone at Craighead, in Ayrshire. They are 

 easily distinguishable from M. cuneata by their beak, which is incurved and not straight, 

 as in the last-named species. 



40. Rhynchonella, sp. ? Sil. Sup., PI. X, figs. 8, 8 a. 



Two single dorsal valves of a Bhyncho?iella not sufficiently complete for specific 

 identification were found by Mrs. R. Gray in the Upper Llandeilo or Balcletchie Con- 

 glomerate at Balcletchie, in Ayrshire ; and of these I have given a figure in order that 

 better and more complete examples may be sought for, so as to permit of a more 

 complete identification. 



4L Rhynchonella Shallockiensis, Dav. Sil. Sup., PI. X, figs. 19, 19 a. 



Marginally sub-pentagonal, slightly broader than long ; dorsal valve very gently 

 convex and much flattened ; surface ornamented with about nine strong ribs, with 

 interspaces of about equal breadth, three of these ribs forming a scarcely raised fold; 

 ventral valve moderately convex ; beak incurved. 

 Length 3, width 4, depth 2 lines. 



Obs. — Of this species Mrs. R. Gray obtained one perfect specimen from the Upper 

 Llandeilo at Shallock Hill, Girvan, Ayrshire. It is so different from the other 

 RlynchoneUa which we meet with in our Silurian rocks that I have ventured to give it a 

 specific name. 



