12 GEOLOGICAL AND NATURAL HISTORY SURVEY OF CANADA. 



zontal dia2)hragms crossing the tubes from side to side. The smaller tubes 

 are crossed by very numerous and close set horizontal diaphragms. 



Its remarkable external characters render this an easily recognized 

 species, and servo to distinguish it from its nearest ally Frasopora affiniSj 

 next described. 



Locality and Formation. — Somewhat rare in the Trenton Formation of 

 Ottawa City. 



Collectors— K Billings, T. C. Weston and Walter R. Billings. 



PRASOrORA AFPINIS. (N. Sp.) 

 Plate III., figs. 2-2c. 



Zoarium discoid, concavo-convex, about 20 mm. in diameter, and about 

 2-5 mm. in thickness in the centre. Upper surface, showing the cell- 

 apertures, gently convex, and quite destitute of monticules. Where the 

 surface is well preserved the cell-apertures are seen to be polygonal j 

 groups of from fifteen to twenty cells, larger than the average, may also 

 bo detected with the aid of a hand-lens. Of the larger cells, from two and 

 a half to three are contained in the space of 1 mm., and of the smaller 

 ones about four. 



We find in tangential sections that the large tubes, which are sub-poly- 

 gonal or rounded in outline, have their interspaces filled with the smaller 

 tubes; these are angular in outline, and consist of only one row of cells 

 around each of the larger tubes, which they do not always completely 

 encircle, the larger tubes being sometimes in contact at limited points of 

 their circumference. 



Longitudinal sections exhibit a very symmetrical arrangement of the 

 two sets of tubes. The larger of these are filled with conical cystoid 

 diaphragms throughout their entire length, (very similar to those of 

 P. oculatd), these are alternate in their arrangement on each side of the 

 visceral chambers, and are sometimes joined to the opposite wall by a 

 straight diaphragm, and sometimes the latter running in an oblique direc- 

 tion downwards or upwards, unite together two of the cystoid diaphragms 

 situated on opposite sides of the tube. Very rarely a straight diaphragm 

 crosses the visceral chamber from side to side. The smaller tubes have 

 numerous complete and horizontal diaphragms, and wherever they cross 

 the tubes there is a slight constriction in the walls of the latter. The 

 present species is distinguished from Frasopora oculata, (I) by the absence 

 of the surface markings so characteristic of that species ; (2) by the fewer 



