398 J. F. BLAKE AND W. H. HUDLESTON ON 



Akca lanthanon, spec. nov. PI. XV. fig. 6. 



Shell elongate, subquadrilateral ; height less than \ the length ; 

 valves obliquely convex ; umbones prominent, approximate, very 

 obliqne, at \ the length from the anterior end ; ventral margin 

 uniformly convex, dorsal margin straight, no area seen ; posterior 

 margin obliquely truncated ; anterior end narrower, sharply convex, 

 posterior portion very slightly flattened ; lines of growth the only 

 ornaments. 



The generic position of this shell is doubtful ; but its similarity 

 to the next, which is undoubtedly an Area, renders this reference 

 probable. 



In the Coral Rag, Slingsby, Yorkshire. 



Arca anomala, spec. nov. PL XY. fig. 7. 



Shell elongate, irregular ; greatest height |- the length ; valves 

 fairly convex ; umbones very oblique, nearly approximate, at I- the 

 length from the anterior end ; ventral margin irregular, convex pos- 

 teriorly, concave beneath the umbones, and rapidly approaching the 

 dorsal margin, posterior end much larger than the anterior, which 

 is produced ; a keel runs from the umbo backwards ; ornaments, 

 concentric ribs following the curvature of the ventral margin. 



In this specimen the teeth of the subgenus Meter oclon are seen. 



In the Coral Rag, at Upware. 



Mytilus varians, Romer. PL XY. fig. 8. 



We figure this, as there may be some doubt if it be Romer 's species. 

 It is common in the North-Dorset district in the higher beds. 



Modiola cancellata, Romer. PL XVI. fig. 5. 



This finely ornamented species presents different appearances 

 according to its preservation. The one figured is from the Upper 

 Calcareous Grit of Nunnington, and is more like what Phillips figured 

 as M. pulchra from the Kelloway Rock. It is not uncommon in 

 the shell-limestones of Highworth, and in the Paringdon district. 



Avicula pteropernoides, spec. nov. PL XVI. figs. 4 & 6. 



The general axis of the shell makes an angle of 40° with the 

 hinge-line. The hinge is f the length along this line ; umbones 

 nearly terminal ; the convexity of the shell gradually declines as it 

 leaves the umbo, till it is nearly flat ; the wing is flat and broad and 

 joins the shell in a uniform curve. Length of hinge 1| inch. 

 When the shell is young it is more uniformly convex and marked by 

 lines of growth. 



It has very much the aspect of a Pteropema, but has not its 

 characters, and its hinge is that of an Avicula. It is very singular 

 that so remarkable a shell should never have been noticed before, as 

 it is rather widely spread, viz. : — in the Upper Calcareous Grit, Wey- 

 mouth ; the Trigonia-heds, Weymouth and Abbotsbury ; Coral Rag, 

 Calne ; Coralline Oolite, Faringdon, and also Thornton, in Yorkshire. 



