Bkkde.] Carboniferous Invertebrates. 73 



a deep rounded mesial sinus, starting near the beak and deepen- 

 ing and widening rapidly to the anterior margin, to which it 

 imparts a distinctly sinuous outline, thus dividing the gibbous 

 part of the valve into two prominent rounded lobes or diverg- 

 ing ridges, separate from each other by a broad rounded de- 

 pression ; ears more or less angular, sometimes extended and 

 acutely pointed, slightly arching, and a little refiexed ; beak 

 rather prominent and recurved ; area moderately developed 

 and common to both valves, but widest in the ventral ; fora- 

 men wide ; cardinal margin provided with four oblique spines 

 on each side of the beak. Dorsal valve following rather nearly 

 the curve of the other, and provided with a mesial ridge corre- 

 sponding to the sinus of the other valve." The interior of the 

 ventral valve possesses a short, sharp mesial septum extending 

 beneath the umbo ; each side of the septum, close under the 

 beak, there is an oval muscular depression, the broader end ex- 

 tending obliquely forward ; near the posterior end is a small 

 elliptical scar. Immediately in front of the scars the shell is 

 smooth. Around the visceral cavity are large pustules, while 

 exterior to these, on the periphery of the shell, are smaller ones 

 arranged in radiating order. There is a small, distinct tooth 

 on each side of the foramen. The deltidial process of the dorsal 

 valve is reenforced by five radiating ridges on the interior of the 

 valve, the first pair of which are nearly parallel to the hinge 

 line, but pointing a little forward and disappearing before reach- 

 ing the margin. Immediately in front of the process, which is 

 somewhat elevated and broad, is a small depression or cavity. 

 The second pair of ridges extend obliquely forward from in 

 front of this cavity. The mesial septum reaches about half 

 way to the front of the shell. On either side of it is the semi- 

 circular brachial area. Pustules on the surface of the valve 

 arranged as in the other valve. " Surface [exterior] of each 

 valve ornamented with about 100 fine, bifurcating, radiating 

 stria>, and sometimes near the front, by a few marks of growth." 

 Length, 9 mm. ; width, 15 mm. ; convexity, 4 mm. 



Range and distribution : Lower and Upper Coal Measures ; 

 6— vi 



