Mesotrypa (?) spinosa.j 



BRYOZOA. 259 



The mesopores are less numerous, and the tabulation of both sets of tubes mote 

 crowded than in M. whiteavesi Nicholson, sp. In M. reguldris Foord, sp., the dia- 

 phragms are few in the zocecial tubes. This is likewise true of M. quebecensis Ami, sp., 

 m which acanthopores seem to be wanting entirely. 



* 



Formation- and locality.— In the middle third of the Trenton shales at Minneapolis, St. Paul and 

 localities m Goodhue and Fillmore counties, Minnesota. 

 Mus. Reg. No. 599.3. 



Mesotrypa (?) spijtosa, n. sp. 



-PLATE XVII, FIGS. 9-12. 



Aspi'dopora parasitica (p&Tt.) Ulrich, 1886. Fourteenth Ann. Rep. Geol.Nat. Hist. Sur. Minn., p. 90. 



Zoarium parasitic, 0.5 to 6.0 mm. thick. Zocecia small, circular, neatly arranged 

 about the clusters, twelve or thirteen of the ordinary size in 3 mm. Interspaces or 

 walls rather thick, but the abundant mesopores shown in thin sections are rarely, if 

 ever, to be made out at the surface. This may be due in part to the large size and 

 prominence of the acanthopores. Internally, with crowded horizontal diaphragms in 

 the mesopores and mostly oblique curved partitions in the zooecial tubes. Sometimes 

 a few at the bottom of the tubes are precisely like ordinary cystiphragms (fig. 12). 



This form seems to hold an intermediate position between M. infida and Aspi- 

 dopora parasitica, differing from the first in having smaller zooecia, thicker walls and 

 stronger acanthopores, and from the second in the greater thickness of the zoarium, 

 much stronger acanthopores, different tabulation of the zocecial tubes, and in but 

 rarely showing the mesopores at the surface, these being, so far as observed, always 

 distinctly visible at the surface of A. parasitica. Atactoporella insueta, another asso- 

 ciated parasitic species, has larger and less regularly distributed zooecia, with smaller 

 and mora numerous acanthopores. 



Formation and locality.— PeihSLps the commonest of the parasitic Bryozoa occurring in the middle 

 third of the Trenton shales at St. Paul, Minneapolis and other localities in Minnesota. 



Mus. Reg. No. 8127. 



Mesotrypa quebecensis Ami, sp. 



FIG. 15, e and /, PAGE 248. 



Diplotrypa quebecensis Ami, 1892. Canadian Record of Science, j). 101. 



Zoarium discoid or subhemispheric, base gently concave, hight 4 to 20 mm., 

 diameter 12 to 45 mm. At Decorah, Iowa, the specimens are generally about 25 

 mm in diameter, and 6 or 7 mm. thick. The same is true of the Kentucky 

 examples, but in New York and Canada they are usually nearly again as large. 



