462 PALEONTOLOGY OF ILLINOIS. 



its mesial or ambulacra! furrow rather wide and deep, and 

 minutely crenate within; transverse furrows well defined, 

 and also minutely crenate. Central hiatus small. So- 

 called ovarian openings small, and those distinct from the 

 anal opening appearing at the surface as four pairs of elon- 

 gate-oval pores. Anal opening comparatively large, and, 

 as usual in the genus, including one of the pores on each 

 side. Surface ornamented with fine parallel stride, running 

 as usual in allied species. 



Hight of one of the smaller, less globose specimens, ex- 

 clusive of the little supplementary base, 0.50 inch; breadth, 

 0.49 inch. Hight of a large more ventricose individual, 

 0.87 inch; breadth of same, 0.84 inch. 



This species has much the form and proportions of the common P. 

 godoni, so much so, indeed, that those who give wide limits to species 

 would probably fail to observe the differences. On comparison, how- 

 ever, it will be found to differ in the following characters, viz : in the 

 first place, its pseudo-ambulacral areas are more convex, and not 

 bounded by near such sharply elevated margins of the radials. Its 

 pore pieces are also larger, and scarcely more than half as numerous 

 as in P. godoni. Its anal and interradial pieces are likewise decidedly 

 smaller than in that species, while it also presents the well marked dif- 

 ference of having its so-called ovarian openings with each pair appear- 

 ing at the surface as two closely approximated, but distinct oval pores, 

 instead of as a single rounded, larger opening. It moreover holds a 

 much lower geological position than P. godoni. 



This is the first true typical Pentremite we have seen with each pair 

 of ovarian pores (so-called) appearing at the surface as two distinct 

 pores. It must be rather rare, as we have only seen three specimens 

 of it. 



Locality and position Upper division of the Burlington group of 

 the Lower Carboniferous, at Burlington, Iowa. No. 387 of Mr. WACH- 

 SMUTH'S collection. 



