CARBONIFEROUS LIMESTONE FOSSILS. 259 



larly instructive by the frequent exhibition of internal cha- 

 racters. 



Not uncommon in the impure carboniferous limestone of 

 Lowick, Northumberland. 



[Col. University of Cambridge.) 



Edmondia rudis (M'Coy). 



Desc. Rotundato-quadrate, very gibbous ; beaks very large, ob- 

 tuse, posterior end broad, subtruncate, very slightly oblique ; 

 posterior slope flattened, steep, undefined ; anterior end sub- 

 truncate, abruptly compressed ; ventral margin gently convex ; 

 hinge-line nearly as long as the shell, slightly raised ; middle 

 of the shell with very unequal rugged plicse, parallel with the 

 ventral margin, anterior and posterior slopes evenly smooth. 

 Length 1 inch 1 line, proportional width -^q^q, width of pos- 

 terior end -f-^Q, length of anterior end y^/^, depth of one 

 valve -^-^— 



The short, quadrate, extremely gibbous form and unequal 

 rugged plicae distinguish this species from all other carboniferous 

 fossils that I know at a glance. There is often a sort of large 

 obscure pitting between the plicae. The cardinal cartilage ridge 

 is very thick, and nearly as long as the hinge-line or simple 

 erect cardinal margin. 



Rare in the impure carboniferous limestone of Lowick, North- 

 umberland. 



{CoL University of Cambridge.) 



Murchisonia dispar (M'Coy). 



Desc. Elongate, very acutely conic ; apical angle 30° ; spire of 

 about eight very gradually increasing tumid whorls having a 

 very thick obtuse prominent band, forming a rounded keel 

 much nearer the lower than the upper suture ; upper and lower 

 surfaces slightly tumid, convex, the lower portion most steeply 

 sloped ; the band is either simple, or rarely with three spiral 

 striae ; two strong spiral lines below the keel, and six slightly 

 smaller ones above it on each whorl ; base of body-whorl 

 rounded, convex, with an obtuse angulation at such a distance 

 below the keel, that it is just concealed by the suture on the 

 spiral whorls ; lines of growth five, unequal, obscure, slightly 

 arched, oblique to the band. Length 7 lines, proportional 

 width y^Q^^, height of last whorl yYo> height of penultimate 

 whorl -2-0- 



This species is easily distinguished from its allies, the M. sub- 

 sulcata and M. Archiacana, De Koninck, and M. Larconi, M^Coy, 



r2 



