New Lower Silurian Bryozoa. 



HELOPORA, Hall. 



I 9 I 



Fig. 15.— Illustrating species of Helopora. a, b and c, H. divaricata, Ulrich, Trenton 

 Shales, Minneapolis, Minn, a, segment, natural size, and x7. b, portion of same 

 xl8. c, transverse section xl8. d, e and/, H. spiniformis, Ulrich, Birdseye limestone, 

 Lebanon, Tenn. d, a segment of the natural size, and its lower half xl8. e, vertical 

 section of lower half. /, transverse section xl8. 



Ml 



i 



Fig. 16.— Illustrating species of Helopora. a and b, two complete segments of H. 

 harrisi, James, xl8, from the upper beds of the Cincinnati group, at Waynesville, O. 

 c, portion of one x50. d, transverse section of a segment x50, showing six rows of 

 zocecia. e, a segment of H. mucronata, n. sp., and most of it magnified to eighteen 

 diameters, showing its slight curve, tapering form, the arrangement, of the zooecial 

 apertures and stria^ above each. /, the lower and most of the upper half of a seg- 

 ment of H. alternata, n. sp., xix. 



