CAMBRO-SILURIAN MICRO-PAL.^ONTOLOGY. 45 



It gives me pleasure to associate with this species the name of Mr. 

 J. F. Whiteaves, the palajontologist and zoologist to the Canadian 

 Surve}^, to whom I am indebted for many favors. 



Stony Mountain, Manitoba, Messrs. T. C. Weston and A. McCharles, 

 1884. 



The position of P. Whiteauesi is, like that of P. magniftca, Miller and 

 Dyer, intermediate between P. maculata, Ulrich, and P. pavonia, 

 D'Orbigny, and such species of the more typical section of the genus, 

 as P. variabilis"^'^ and P. plumaria, James. The longitudinal arrange- 

 ment of the zooecia on the elevated median portion of the frond distin- 

 guishes it from the former species, while it agrees with them and differs 

 from the latter group in having clusters of large cells, and in the 

 circumstance that the apertures of the zooecia are usually arranged 

 in an intersecting manner over the lateral portions of the zoarium. 

 Among species having hexagonal or rhomboidal zooecia, P. magw'fica 

 forms a broad expansion, the surface of which is elevated at rythm- 

 ical intervals into small conical monticules, the apices of which are 

 generally solid. Similar monticules are present on P. plumaria and on 

 old examples of P. variabilis. In all three of these closely related 

 species the zooecia are also a little smaller than those of P. Whiteavesi. 



Arthroclema angulare, Ulrich. 



Arthroclerna avgulare, Ulrich, Kept. 111. Geol. Sur., vol. 8, pi. 29, figs. 6-6b (in 

 press.) 



Several segments, agreeing closely with the Illinois types of this 

 species, were noticed on slabs from Stony Mountain, collected by Dr. 

 E. W. Ells in 18^5 and by Mr. Weston, in 1884. 



Helopora Harrisi, James. 



Helopora harrisi, James, 1883, The Palseoctologist, No. 7, p. 59, pi. 2, figs. 2-26. 



Associated with Sceptropora facula and Arthoclema angulare, I find 

 a number of very slender segments of a jointed zoarium which, though 

 not in a very good state of preservation, may still be referred to this 

 species with much confidence. They are much more delicate than 

 those 0^ Arthroclerna angulare^ being about four mm. long and 0*25 mm. 

 in diameter, with five or six rows of narrow elliptical zoa^cia apertures. 

 The species cannot be recognized from Mr. James' figures, but full 



* This name is proposed instead of P. nodosa, James, figured in my "American Palaeozoic 

 Bryozoa," (Jour. Cin. Soc. Nat. Hist., vol. 5, .pi. 7, fig. 2), the specific name having been pre- 

 occupied by Hall in 1847 {Eschampora nodosa). The specimen figured by me is an old one, 

 young examples being much more slender, and often entirely without monticules. 



