170 Prof. F. M'Coy on some new Mountain Limestone Fossils. 



Common in the carboniferous limestone of Beith, Ayrshire ; 

 rare in the carboniferous limestone of Derbyshire. 

 {Col. University of Cambridge.) 



Pteronites persulcatus (M'Coy). 



Sp. Char. Transversely trigonal, right valve gently convex, left 

 valve diagonally tumid, posterior end broad, rounded, flattened 

 anterior end and beaks forming a small, convex, obtusely 

 pointed extremity ; a small space of the anterior extremity 

 smooth, all the rest of the shell covered with small, coarse, 

 rugged, flexuous, irregular ridges, for the most part alternately 

 larger and smaller, and less than their thickness apart, those 

 of the posterior wing nearly straight, radiating, those of the 

 body arching downwards towards the ventral margin. Length 

 of hinge 10 lines, greatest depth at right angles to the hinge 

 5i lines. 



This species is distinguished from the P. sulcatus (M'Coy) and 

 the P. semisulcatus (M'Coy) (of which latter it has the exact 

 form) by having all the posterior part of the shell striated ; in its 

 ridging it agrees with the Lanistes rugosus (M'Coy, Synop. Carb. 

 Foss. Ireland, t. 10. f. 8), but the above form, and broad beak 

 and anterior end seem to separate the latter. It grows larger 

 than the above measure. 



Not uncommon both in the main limestone of Derbyshire and 

 the black limestone resting on it : of large size in the impure 

 limestone of Lowick, Northumberland. 

 [Col. University of Cambridge.) 



Streblopteria (M'Coy), n. g. 

 Etym. (TTpe^Xo<i, perversus, and Trrepov, ala. 



Gen. Char. Ovate or rounded, obliquely extended towards the 

 anterior side; posterior wing broad, undefined, nearly rec- 

 tangular, extending nearly as far as the posterior margin of 

 the shell ; anterior ear small, deeply defined ; surface smooth 

 or radiatingly ridged; one large, faintly marked muscular im- 

 pression a little -behind the middle ; one short, narrow tooth 

 slightly diverging from the hinge-line on the posterior sides 

 of the beaks ; ligament confined to a narrow simple facet on 

 the hinge-margin. 



These shells differ from some of the short-winged group of 

 Avicula (or Pteria), to which they are most allied, by the obli- 

 quity of the body of the shell being towards the anterior instead 

 of the posterior side — the reverse, in fact, of what occurs in nearly 

 all shells except the Limce. There are many species in the car- 

 boniferous limestone, to which formation the genus seems at pre- 



