163 



transverse sections or by grinding down the surface, polygonal : mesopores 

 smaller and more distinctly angular, either occupying the interstices of 

 the zooecia or forming numerous isolated clusters or maculae, which are 

 irregular in shape but nearly equidistant, their maximum diameter being 

 about one millimetre and their distance apart averaging about four mm. : 

 acanthopores apparently absent. Longitudinal sections shew that the 

 zooecia are provided with about thirty continuous and usually straight or 

 slightly concave diaphragms in the space of five mm., and that the 

 diaphragms in the mesopores are nearly twice as close together as those 

 of the zocecia, but otherwise similar to them. 



East Selkirk, L. M. Lambe, 1890 : a few remarkably well preserved 

 but imperfect specimens. 



These specimens seem to indicate a new species, which appears to differ 

 from M. Quebecensis ( = Biplotrypa Quebecensis, Ami*), by its nearly 

 equidistant and clearly defined maculse or clusters of mesopores, and from 

 M. infida, Ulrich, "f" by the same character, coupled with the absence of 

 acanthopores. 



DiPLOTRYPA Westoni, Ulrich. 



Diplotrypa Westoni, Ulrich 1889. Geol. Surv. Canada, Contr. Micro- 

 Pal. Cambro-Silur. rocks, etc., pt. 2, p. 30, 

 pi. 8, figs. 4, and 4, a-h. 



Big Island, Lake Winnipeg, T. C. Weston, 1884: one specimen, the 

 type of the species, which latter is said to be " very nearly related to the 

 European Diplotrypa petropolitana (Pander)." 



BYTHOTRypA LAXATA, Ulrich. 



FistuUpora (?)laxata,'[Jlvic\i 1889. Geol. Surv. Canada, Contr. Micro- 

 Pal. Cambro-Silur. rocks, etc., pt. 2. p. 37, 

 pi. 8, figs. 2, and 2a. 



Bythotrypa laxata, Ulrich 1893. Lower Silur. Bryoz. Minn., p. 325, 



pi. 28, figs. 21-25. 



Lower Fort Garry (St. Andrews), Dr. R. Bell, 1880; one large 

 specimen. 



* Canadian Record of Science, vol, V. (1893), p. 100 ; and, Ulrich, 1893, Lower Silurian 

 Bryozoa of Minnesota, p. 259, and figs. 15, e-f, on p. 248. 

 t Lower Silurian Bryozoa of Minnesota, p. 258, pi. 17, figs. 1-8. 



3i 



