BRYOZOA. 525 



tures; walls thick, ring-like; two or three diaphragms developed. 

 Interzooecial space at first occupied by vesicular tissue, which 

 afterwards becomes obsolete. In tangential sections the minute 

 tubuli are quite inconspicuous (only in longitudinal series), and 

 the maculae have a solid appearance. 



The large subfrondescent growth, and thick ring-like walls, 

 distinguish it with other characters from P. splendens and P. 

 firma. 



Position and locality: Cincinnati group; Wilmington, 111. 



PACHYDICTYA FERMA Ulrich. 



PL XXXI, fig. 2-2f. 



Zoarium consisting of usually twisted, compressed branches, 

 5 to 10 cm. in height, 10 to 15 mm. in width and 5 to 8 

 mm. in thickness. Transverse section lenticular. Surface gen- 

 erally marked with small, conical monticules, with solid apices, 

 arranged in quite regular diagonal intersecting series. Zooecial 

 tubes gradually curving outwards until they are nearly direct 

 at the surface, provided with an occasional diaphragm. Zocecia 

 surrounded by one or two series of minute tubuli which appear 

 as granules upon the surface when well preserved. Apertures 

 with but little regularity of arrangement, sometimes subcircu- 

 lar, usually oval, from 0.15 to 0.20 mm. in diameter, about six 

 in two mm. measuring lengthwise. Maculae subsolid with a 

 variable number of minute tubuli aggregated in them. Inter- 

 zooecial space provided in the deeper portions -with vesicular 

 structure. This is afterwards replaced with solid calcareous 

 tissue. 



The comparatively thick branches, small pimple-like monti- 

 cules, large number of granules, and lack of orderly arrange- 

 ment of the apertures, (though sections show the zooecia to be 

 arranged in longitudinal series), are the most marked charac- 

 ters of this species. In the width of the branches it resembles 

 P. robust a, but ample differences in cell arrangement distinguish 

 them. 



Position and locality: Cincinnati group, Wilmington, 111. 



