BRYOZOA. 461 



tervals. Surface marked with very slightly elevated aggrega- 

 tions of larger cells surrounding a larger or smaller cluster of 

 mesopores, about three mm. apart. Zooecial walls but little 

 thickened in the peripheral region. Mature portion of the 

 zooecial tubes usually longer than the immature portion; the 

 bend in the tubes is rather abrupt. Zooecia subpolygonal, about 

 seven in two mm., with subcircular apertures; the diameter of 

 the smaller apertures is about 0.2 mm., of the larger, constitut- 

 ing- the borders of the clusters, about 0.35 mm. A few meso- 

 pores scattered about irregularly among the zooecia, usually 

 gathered into clusters of from six to fifteen in the centre of a 

 group of the larger sized zooecia. Diaphragms present through- 

 out the zooecial tubes, some horizontal, some incomplete, vary- 

 ing in separation, in the axial region somewhat more than a 

 tube diameter distant, in the cortical region from one-third to 

 one-half of a tube diameter apart. Acanthopores (?)very small. 



Sections of this form present some very interesting features. 

 In the axial region the diaphragms extend horizontally across 

 the tubes but in the mature region, they are incomplete and 

 crescentic in shape, rarely, if ever, extending more than half 

 way across the tube. In tangential sections another peculiarity 

 is brought out, namely, at the angles between the zooecial tubes, 

 there is a space, generally triangular in shape, of lighter color 

 than the remainder of the interspaces or wall. The points of 

 these spaces continue as dark lines that mark the divisional 

 line between the walls of adjoining zooecia. The walls exhibit a 

 horizontally lined appearance reminding one very much of the 

 wall structure observed in some of the CERAMOPORHXE (e. g. 

 Crepipora). In exceptionally good tangential sections minute 

 circles may be detected between the zooecial walls. They have 

 the appearance of minute thin-walled tubuli, and, though much 

 smaller than usual, are probably equivalent to the peculiar 

 acanthopores of this genus. 



This species resembles B. ottawense Foord, in the possession 

 of incomplete diaphragms and the peculiar structure of the 

 walls, but differs in the closer arrangement of the tubercles, the 

 thinner walls, and inconspicuous acanthopores. 



Position and locality: Cincinnati group, Wilmington, 111. 



