54 SYNOPSIS OF THE CHARACTERS OF THE 



Venus tenuistriata. MCoy. (PI. VIII. fig. 10). 



Sp. Ch. — Suborbicular, slightly transverse, convex; anterior side and front margin rounded; posterior end 

 subtruncate, rounded, beaks prominent ; surface roughened by very close, fine, concentric strice ; a deep sinus in 

 the palleal impression. 



This rare species is but slightly convex ; the beaks are large, the anterior side short and rounded, the dor- 

 sal margin is slightly convex, the transverse striae are very fine and closely placed ; the sinus in the impression of 

 the mantle is very deep, with parallel sides, rounded at the end. Length one inch three and a half lines, width 

 one inch seven lines. 



PULLASTRA ANTIQUA. SoW. 

 Pullastra antiqua. Sow. Geol. Trans. 



The specimens which have occurred of this species are too imperfect for description. 



Pullastra bistriata. Portk. 



Pullastra bistriata. Portk. Geol. Eep. 



Sp. Ch. — Transversely elliptical, oblique, slightly convex, flattened in the middle ; beaks small, close to 

 the anterior end ; anterior side very short, rounded, posterior end obliquely subtruncate ; hinge-line straight, 

 three-fourths the length of the shell ; shell girt with about ten concentric step-like ridges, rounded on their ven- 

 tral edge, flattened above, each beautifully sculptured with close, rounded, prominent zig-zag lines. 



This beautiful shell is exceedingly common in the cai'b. slate of several districts in Ireland ; it is distin- 

 guished by the peculiar sculpturing of the surface from any other fossil. Length three lines, width seven 

 lines. 



Pullastra crassistria. M'Coy. (PL XI. fig. 7). 



>^^. Ch. — Transversely oval, very gibbous; dorsal and ventral margins equally convex; anterior and pos- 

 terior ends nearly equal, rounded, subtruncate ; sui-face closely marked with unequal, obtuse, concentric 

 ridges. 



This little species is remarkable for its equal convexity, thick, regular, transverse striae. Length five lines, 

 width nine lines. 



Pullastra elegans. M'Coy. (PI. VIII. fig. 16). 



Sp.Ch. — Transversely oblong, gibbous; length two-thirds the width; front margin and hinge-line straight 

 and nearly parallel ; anterior side very short, rounded ; posterior end truncated ; posterior slope separated from 

 the body of the shell by a large, obtuse, diagonal, rounded ridge from tlie beak ; surface marked with fine, regu- 

 lar, transverse striae, having between them broad, flat, regular, smooth spaces, parallel with the margin. 



There is a peculiar squareness of contour in this shell, resulting from the abrupt truncation of the posterior 

 end, and the straight and nearly parallel dorsal and ventral margins ; although very gibbous, the front is flat- 

 tened, as is also the posterior slope, the separating ridge being obtusely rounded, the beaks large and tumid ; 

 the form is strongly allied to some of the tertiary species oi Petricola. Length ten lines, width one Inch 

 one line. 



Pullastra elllptica. Pliil. sp. 



Venus elllptica. Phil, Geol. York. 



Sp.Ch. — Transversely elHptical, convex; surface with broad, concentric undulations. 

 Length six lines, width nine lines. 



