564 PALEONTOLOGY OF ILLINOIS. 



HEMITRYPA PERSTRIATA Ulrich. 



PL LVII, Figs. 6-6a. 



Zoarium infundibuliform, strongly folded in the upper half, 

 slowly expanding, 5 cms. or more in height, non-poriferous on 

 the outer side. Superficial net-work with the interstices or 

 openings circular, comparatively small, surrounded by a sloping 

 area, generally hexagonal, sometimes pentagonal or quadrate 

 in outline, about twenty in 5 mm.; the bars and scalse sub- 

 equal and sharply carinate. On the reverse the branches are 

 rounded, with from three to six strong longitudinal striae, and 

 from one to three series of small but prominent spines, the cen- 

 tral row being usually the most conspicuous. Average width 

 of branches about 0.3 mm.; just before bifurcation at least 0.5 

 mm., with ten or eleven in 5 mm. Bifurcations remote. Dis- 

 sepiments very short, much depressed, about half as wide as 

 the branches. Fenestrules narrow, oblong oval, about 0.5 by 

 0.15 mm., and fourteen or fifteen in 1 cm. 



The favose net-work is very much like that of H. pateriformis, 

 but the reverse aspect of the two species is very dissimilar. The 

 zoarium of that species is also smaller and plate-shaped rather 

 than infundibuliform. The narrow fenestrules and strongly 

 striated branches distinguish the species from H. plumosa, Prout, 

 and H. proutana. 



Position and locality: Keokuk group, Bentonsport and 

 Keokuk, Iowa. 



HEMITRYPA PATERIFORMIS Ulrich. 



PL LVII, Figs. 7-7c. 



Zoarium patelliform, spreading rapidly from the short and 

 strongly ridged footstalk. It is further supported by numerous 

 root-like processes which extend downward from its under side 

 near the base. On the obverse or upper face, the bars forming 

 the superficial net work are carinated, the principal ones often 

 a little the strongest, the interstices regularly circular, rather 

 small, and alternating in adjoining rows, with about twenty- 

 one in 5 mm. On the reverse the fenestrules are sub-circular 



