Limestone Fossils. 189 



Fragments of this species might be taken for a Solen, and the 

 S. siliquoides (Kon.) may have some affinity with it, though spe- 

 cifically distinct. The muscular impression is rather large, 

 though superficial, quadrato-reniform, rather behind the middle 

 of the length, and nearer to the cardinal than the ventral margin. 



Specimens of the above large size, rare in the carboniferous 

 limestone of Derbyshire ; specimens about 3 inches long, and 

 slightly more convex, in the carboniferous limestone of Lowick, 

 Northumberland. 



{Col. University of Cambridge.) 



Cardiomorpha orbicularis (M'Coy). 



Desc. Suborbicular ; anterior end moderately large, semicir- 

 cular, compressed ; ventral and posterior margin very convex, 

 regularly curved; posterior side small, rounded, gradually 

 compressed ; beaks very large, tumid, obliquely inrolled to- 

 wards the anterior end, projecting greatly beyond the hinge, 

 nearly over which is the deepest part of the shell ; valves be- 

 coming gradually flattened towards the margins; surface 

 smooth, even ; substance of the shell very thin ; hinge-margin 

 inflected at right angles, forming a cartilage support rather 

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

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

 end yL%, width half-way between the beak and posterior end 

 y^Q^Q, depth (greatest near the beak) -^-^q. 



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 (M'Coy), 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 



