10 GEOLOGICAL AND NATURAL HISTORY SURVEY OF CANADA. 



HOMOTRYPA SIMILIS, (N. Sp.) 



Plate II., figs. 2-2d, 



Zoarium ramose, consisting of small sub-cylindrical, or compressed 

 branches. Branches from 8 to 15 mm. in their greatest diameter. Sur- 

 fiicc smooth, with groups of larger cells than the average occupying small 

 areas, very slightly raised above the general surface of the zoarium. Of 

 the ordinary sized cells there are about four in the space of 1 mm., of 

 the larger ones, (that is, those occupying the slightly raised portions of 

 the surface), about three; In well preserved specimens the surface pro- 

 jections of the spiniform tubuli may be detected with the aid of a hand 

 lens. 



In tangential sections the tubes are seen to be thin walled and polygonal 

 in outline in the axial region, and to become thickened near the surface, 

 where spiniform tubuli arc developed at the angles of junction of the cell- 

 walls. 



In longitudinal sections the tubes are first parallel to the axis of the 

 zoarium, but as they approach the surface they bend gradually outwards. 

 A moderate number of horizontal, straight, or slightly curved diaphragms, 

 from one-half to two tube diameters apart, intersect the tubes for the 

 greater portion of their length, till on nearing the surface cystoid dia- 

 phragms are developed. These diaphragms are conspicuous in tangential 

 sections, in which they appear as straight or curved lines crossing the 

 cell-apertures J sometimes two of these lines are visible in the same cell- 

 aperture, owing to their overlapping each other. The present species is 

 very closely allied to Homotrypa obliqua, Ulrieh, from which it differs in 

 its smooth surface and more conspicuous spiniform tubuli. 



Locality and Formation, — Ottawa City. Trenton Formation. 



Collector. — E. Billings. 



pRASOPORA, Nicholson and Etheridge, jun. 



" Free, or loosely adhering to foreign objects, forming hemispherical 

 liiasses, or thin expansions, with a wrinkled epitheca covering the lower 

 surface. Tubes cylindrical or prismatic, and having one or both sides 

 lined with cystoid diaphragms. Interstitial tubes often completely 

 isolating the proper zooecia, and crossed by numerous diaphragms. Spini- 

 form tubuli sometimes nearly absent, in other cases more numerous. 

 I'renton and Cincinnati.'* (E. O. Ulrieh, journ. Cincinnati Soc. Nat. 

 Hist., Vol. y., p. 153, 1882.) 



