562 PALAEONTOLOGY OF ILLINOIS. 



and have a sub-circular opening at the distal extremity. At 

 present I cannot give a satisfactory explanation of their nature. 

 Position and locality: Warsaw beds at Warsaw, 111. 



HEMITRYPA PROUTANA var. NODULOSA n. var. 



PL LVII, Fig. a-2c. 



This form differs from the typical H. proutana in having the 

 interstices of the superficial net-work decidedly rayed or flori- 

 form, the small denticles which project from the sides of the 

 bars being more numerous and better developed. On the reverse 

 the branches are somewhat thinner, rounded, and bear numer- 

 ous small tubercles. The zoarium also does not attain the size 

 of H. proutana, but in the other measurements the variety 

 offers no striking difference. 



Position and locality: Keokuk group, Keoktfk and Bentons- 

 port, Iowa, and Nauvoo, 111. 



HEMITRYPA NODOSA Ulrich. 



Pl.LVn.Fig.3. 



The principal distinguishing feature of this species is the 

 nodose enlargement on the reverse of the branches opposite their 

 junction with the dissepiments. The branches are rounded, 

 eleven or twelve in 5 mm., with an average width of 0.2 mm., 

 increasing from 0.15 to 0.3 or 0.4 mm. before bifurcation, the 

 dissepiments depressed, and less than half the width of the 

 branches; the fenestrules oval or sub-quadrate, twice as long as 

 wide, as wide as the branches, and seven or eight in 5 mm. 

 The superficial net-work is very much like that of H. proutana, 

 but the interstices are more nearly circular, about twenty in 

 5 mm., and the principal and secondary bars of about equal 

 strength. 



The strong nodes and more slender branches distinguishes the 

 species from H. plumosa Prout sp. The specimen of which 

 several branches are represented by fig. 3a, simulates this species 



