of the Rocks associated with the Coal of Australia. 301 



Pachydomus carinatus (Mor.). 

 Abundant in the fine sandy schists of Wollongong, N. S.Wales ; 

 more rare in the white rock of Port Arthur, V. D. Land. 



Pachydomus globosus (Sow. sp.). 

 Common in the sandstone of Wollongong, N. S. Wales. 



Pachydomus gigas (M'Coy). PI. XVI. fig. 3. 

 Sp. Char. Transversely oval, length two-thirds of the width, very 

 gibbose, inflated ; beaks very large, incurved, placed in about 

 the anterior third of the shell ; posterior side obliquely trun- 

 cated, the angles rounded; posterior slopes compressed, flat- 

 tened ; posterior ridge obtusely rounded, almost disappearing 

 before reaching the posterior inferior angle; anterior side 

 small, narrowed, with a slightly marked sinus between it and 

 the convex ventral margin ; surface marked with small con- 

 centric cord-like sulci and ridges. 



This is distinguished from the P. globosus (with which Mr. 

 Morris seems to include it) by its greater width in proportion to 

 the length, by the flattened, compressed sides of the posterior 

 slopes and the more oblique truncation of the posterior end, and 

 the smallness and narrowed appearance of the anterior side, 

 arising from a slight, but always perceptible, sinus between it and 

 the convexity of the ventral margin. The shell is very thin in 

 this species, which makes a near approach to Leptodomus (M'Coy) 

 in all its characters. Length 4^ inches, width 6 inches 3 lines 

 (often much larger). 



Common in the fine sandstone of Wollongong, N. S. Wales. 



Pachydomus sacculus (M'Coy). PI. XIV. fig. 5. 



Sp. Char. Subquadrate or satchel-shaped, length nearly equalling 

 the width, thickness two-thirds the length ; gibbose towards 

 the beak, compressed towards the ventral margin ; beaks large, 

 nearly central, strongly incurved towards the anterior side ; 

 posterior side forming a short, compressed, rectangular wing ; 

 anterior side very obliquely truncated ; anterior and posterior 

 slopes abruptly rounded, and the angles formed by their junc- 

 tion with the ventral margin equal, broadly rounded and nearly 

 equidistant from the beak ; abdominal margin broadly concave, 

 giving the middle of the valves a flattened, slightly hollowed 

 appearance ; shell very thick, foliaceous ; surface with a few 

 obtuse concentric elevations and numerous irregular concentric 

 lines of growth. 

 Length 4J inches, width 4 inches 9 lines. I am uncertain 



whether the specimen figured is from Black Head or Wollongong, 



N.S.Wales. 



