, . BEYOZOA. 257 



esotrypa.l 



Internal characters : These are sufficiently illustrated on plate XVII, but it is well 

 to state that a few tubes in both vertical and tangential sections may show a single 

 cystiphragm at the bottom. Diaphragms are wanting, as are acanthopores also. 



This beautiful bryozoan is a true Aspidopora, and is rather closely related to 

 A. newberryi Nicholson, sp,, the only reliable or constant difference between them 

 being in the number of cystiphragms. In the present species these structures are so 

 few that they may appear to be wanting entirely, but in Nicholson's species they 

 occur in every zooecial tube, numbering in each, according to age, from one to ten. 

 Several discoidal forms are to be found in the same beds with A. elegantula, but none 

 of them are sufficiently like it to render confusion probable. 



Formation and locality. — Kather rare in the Galena shales at St. Paul, and near Kenyon, Goodhue 

 county, Minnesota. 



Mus. Beg. No. 8126. 



Genus MESOTRYPA, n. gen. 



Diplotrypa (part.) Nicholson, 1879, Pal. Tab. Cor., p. 312, and 1881, The Gen. Monticulipora, pp. 101 



and 155. 



Zoaria hemispheric, conical, or discoidal, generally free, with the lower surface 

 covered by an epitheca. Zocecial tubes prismatic or cylindrical, more or less sep- 

 arated from each other by angular mesopojres ; internally with oblique and some- 

 times funnel-shaped diaphragms, that often simulate and probably are to be regarded 

 as peculiarly modified cystiphragms. Mesopores becoming smaller with age, inter- 

 sected by numerous diaphragms. Acanthopores generally present, sometimes of 

 large size. 



Type : Diplotrypa infida Ulrich. 



This genus is established for a natural group of species heretofore referred, 

 erroneously, L believe, to Diplotrypa*. These species are D. regularis Foord, D. que- 

 becencis Ami, D. whiteavesi Nicholson, D. patella Ulrich, the type D. infida, and three 

 new species, M. discoidea, M. rotunda, and M. (?) spinosa. To these might be added the 

 Niagara D. milleri Ulrich, but as the position of that species is somewhat in doubt, 

 it had best be left as originally placed till an opportunity offers to rework the type 

 specimens. 



The affinities of the proposed genus are not with Diplotrypa but with Prasopora. 

 Indeed, for some time I considered the propriety of referring the group to Prasopora, 

 yet after mature reflection the erection of a new genus was decided upon as serving 

 the purposes of classification better than would have been done by extending the 

 limits of that genus. 



'"ii'ee part li, Oontrl. Miero-Pal. Cambro-Sii. Rocks, Can., p. 32, 1890. 

 -17 



