CAMBllO-SILURIAN MICRO PALAEONTOLOGY. 13 



number of its small tubes, and their less numerous diaphragms. It may 

 be separated from P. Selwyniij Nicholson, by the much smaller size of its 

 zoarium, and by the smaller number of its interstitial tubes, which arc 

 not " collected into stellate groups or macuhc." 



Locality and Formation, — Ottawa City. Trenton Formation. 



Collector —A. II. Foord. 



Prasopoha Selwynii, Nicholson. 



Moniiculipora (Frasopora) SelwynU,l^ichohon, "The genus Monticulipora," 

 p. 206, figs. 44 and 45, 1881. 



This species is very abundant throughout the Trenton Formation in 

 Canada. It has recently been found also in the uj:)pcr beds of the Chazy 

 formation, at Nepean, near Ottawa City. It is figured, but not described, 

 by Billings in the ''Geology of Canada," (p. 15G, fig. 11*7,) a-s Stcnopora 

 petroiyjlltana ^ Pander. 



DiPLOTRYPA, Nicholson. 



" Zoarium free, hemispherical. Spiniform tubuli often present, though 

 never numerous.* In other respects like Frasopora, excepting that the 

 tubes are provided with straight diaphragms only. Trenton and Niagara." 

 (E. 0. Ulrich, Journ. Cincinnati Soc. Nat. Hist., Vol. V., p. 153, 1882.) 



DiPLOTRYPA REGULARIS. (N. Sp ) 

 Plato I., figs. 3-3c. 



Zoarium discoid, with attenuated edges, greatest diameter about 20 mm., 

 and from one and a-half to two mm. in thickness in the centre; tubes 

 directed upwards nearly at right angles to the basal plate, and opening 

 upon the surface of the zoarium, which is strongly convex. Surface 

 apparently destitute of monticules. Cells of two kinds; largo and small ; 

 the former rounded to sub-polygonal in outline ; of these there are groups 

 at intervals somewhat larger than the rest, about two in the space of 1 

 mm., of the others about three and a-half are contained in the same 

 space. 



In tangential sections the large or proper cells (excluding those which 

 exceed the average dimensions) are very uniform in size and shape, and 

 are in contact only at limited points of their circumference, this limitation 



* This sentence reads in the original " no spiniform tubuli." The writer called 

 Mr. Ulrich's attention to this inadvertence, and he has supplied the words now 

 inserted. 



