Monotrypa intabulata.] 



BRYOZOA. 



305 



MONOTRYPA INTABULATA, n. sp. 



Compare Monotrypa rectimuralis ULKICH, 1890, Gool. Sur. 111., vol. viii, p. 462. 

 b 



FIG. 20. Monotrypa intabulata, n. sp. Upper half of Galena shales, Goodhue and Fillmore counties, 

 Minnesota. Collection of E. O. Ulrich. a, transverse section, x!8, showing subequal size of tubes, their 

 thin walls, and the lucid spot in the angles of junction ; 6, vertical section, xlS, the tubes filled chiefly 

 with clayey matrix ; c, transverse section, x!8, of a variety from Fountain, Minnesota, provisionally 

 referred to this species. It has larger zooecia than usual, while the size of the latter seems also to be 

 rather less equal. 



Zoarium forming subhemispherical or depressed-spherical masses, generally 

 between 30 and 60 mm. in diameter and 15 to 30 mm. in bight ; lower surface 

 usually less convex than the upper and sometimes partly covered by an epitheca. 

 Celluliferous surface even, covered with subequal, thin walled, polygonal zocecial 

 apertures, of which the usual number in 3 mm. is between eight and nine. In sev- 

 eral small examples found near Fountain, the number is between seven and eight. 

 Conspicuous and regularly arranged clusters of large cells are wanting, though here 

 and there one or several zocecia may be of unusual dimensions. 



Internal characters: In transverse sections the walls are exceedingly thin, but 

 where well preserved their duplex character is determined by minute triangular, 

 seemingly open spaces at the angles of junction, formed by the separation of the 

 walls of adjoining tubes. Here and there a young zooecium is met with, but true 

 mesopores and acanthopores as well, are unquestionably wanting. In vertical sec- 

 tions the walls form nearly straight lines ( merely curving to adapt themselves to the 

 growth of the zoarium) being entirely without the crenulations so characteristic of 

 the typical species of the genus. Diaphragms also seem to be wanting, and most of 

 the tubes of specimens from shaly strata are in great part filled with the matrix. 



At first I believed this species must be the same as the M. rectimuralis Ulrich, 

 the types of which were collected from nearly equivalent beds in southern Illinois. 



The absence of diaphragms was explained by the supposition that they had been 

 -20 



