BRYOZOA. 523 



PACHYDICTYA EVERETT: Clrich. 

 PL xxxm. flg. i-if . 



Zoariuin an undulated frond, several cm. in height and width, 

 three mm. or a little more in thickness. Surface smooth, desti- 

 tute of maculae. Cell apertures suboval to hexagonal in shape, 

 forming diagonally intersecting as well as longitudinal rows, 

 from 0.18 to 0.25 mm. in longitudinal diameter, about five in 

 two mm. diagonally, and four longitudinally. Occasionally a 

 cell aperture has preserved an opercular structure. Zooecial 

 tubes rather thin-walled, largely in contact, with no straight 

 or flexuous lamella separating them, provided with closely set 

 diaphragms. The interstitial vesicles are angular, comparatively 

 few, mainly occupying the angles between the zooecia and re- 

 maining so far as observed, open to the surface. In deep tan- 

 gential sections the walls are exceedingly thin and appear to 

 contain a series of exceedingly minute tubuli. The minute 

 tubuli between the median laminae of the frond are a more de- 

 cided structure than in any other species of the genus yet ex- 

 amined. 



This species preserves all the essential characters of the genus, 

 yet the open interstitial spaces and the great abundance of dia- 

 phragms are curious features. The smooth surface unmarked 

 with maculae, and the regular and comparatively large sized 

 sub-angular cells distinguish it from other species of the genus. 



Position and locality: Trenton group; Dixon, 111. 



PACHYDICTYA SPLENDENS Ulrich. 



PL XXXI, flg. 2g, and PL XXXH, flg. 1-lb. 



Zoarium consisting of undulated flabellate fronds, or of broad 

 irregular dividing branches, 1 to 3 cm. wide, as much as 15 

 cm. high, and 4 mm. or less in thickness. Surface smooth with 

 scarcely noticeable clusters of cell apertures separated by thicker 

 interspaces and a little more prolonged than ordinarily. Cell 

 apertures oblique, narrowing toward the upper end, with peri- 



