BRYOZOA. 259 



Mesotrypa (?) spinosa.] 



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







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

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

 in which acanthopores seem to be wanting entirely. 



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

 localities in Goodhue and Fillmore counties, Minnesota. 



Mus. Reg. No. 5993. 



MESOTRYPA (?) SPINOSA, n. sp. 



PLATE XVII, FIGS. 0-12. 



Aspidoporaparasitica(i>a.rt,.)Ui,Ricn, 1886. Fourteenth Ann. Rep. Geol.Nat. Hist. Sur. Minn., p. 90. 



Zoarium parasitic, 0.5 to 6.0 mm. thick. Zooecia 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 zocecia,, thicker walls and 

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

 much stronger acanthopores, different tabulation of the zooecial 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. Atadoporella insueta, another asso- 

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

 and more numerous acanthopores. 



Formation and locality. Perhaps 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 /, PAGF. 248. 



Diplotrypa quebecensis Ami, 1892. Canadian Record of Science, p. 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. 



