258 CARBONIFEROUS LIMESTONE FOSSILS. 



less than 2 lines wide. Length 3 inches 2 lines^ proportional 

 width from beak to ventral margin -f^-^, length of anterior 

 end -^j^Q, width half-way between the beak and posterior end 

 -^Q^jj, depth (greatest near the beak) -^^^, 



This is only likely to be confounded with the C. oblonga 

 (Sow. sp.), but is distinguished by its large anterior and small pos- 

 terior sides, extremely large beaks, and flattened orbicular valves. 

 The young of the C. corrugata (]VPCoy), which is nearly like in 

 form, is distinguished by the large corrugations of the sides. 



Seems not uncommon in the carboniferous limestone of Der- 

 byshire. 



{CoL University of Cambridge.) 



Lithodomus Jenkinsoni (M^Coy). 



Desc, Longitudinally oblong or oval, subcylindrical ; beaks 

 small, much incurved, obliquely inrolled over the wide, deep, 

 cordate, anterior lunette ; anterior end very short, extending 

 very slightly in front of the beaks, obtusely rounded ; poste- 

 rior end slightly wider than the anterior, obtusely rounded ; 

 dorsal margin nearly straight, gradually rounding into the 

 posterior end; ventral margin very slightly convex; valves 

 evenly tumid, most so along an undefined line from the beaks 

 to the respiratory margin a little in front of the middle of the 

 length; surface with irregular, coarse, concentric lines and 

 plicae of growth. Casts show the large anterior and posterior 

 adductor impressions distinctly connected by the simple pallial 

 scar, together with faint traces of the concentric plicse of the 

 surface, crossed by microscopic, close, diagonal strise from the 

 beaks towards the respiratory margin ; also an impression of 

 the small cartilage ridge within the dorsal margin. Length 

 1 inch 7 lines, proportional depth greatest at middle of length 

 Y^jy^y, depth at posterior end y^^^^, from apex of beaks to ventral 

 margin y^^^y, length and width of anterior lunette y^/q, greatest 

 depth of both valves yVo? l^^g^h of anterior end y^^^ . 



This is a smaller and much more obtuse species than the 

 L. dadyloides (M^Coy), the anterior end being proportionally 

 broader and more obtusely rounded ; the posterior end is also 

 less pointed, and the anal angle not elevated. 1 have not seen 

 the external shell of this species, except near the margins, and 

 here there is no trace of the distinct longitudinal or radiating 

 striation of that species, traces of which are however seen on the 

 internal casts. I dedicate this species to the Rev. Mr. Jenkinson 

 of Lowick, to whose labours we owe the most extensive and 

 beautifully perfect local collection perhaps ever made — particu- 



