BRYOZOA. 493 



CYSTODICTYA HAMILTONENSIS Ulrich. 



PI. XLII, flg. 4. and PI. XLHI, flg. 1. 



Zoarium a bifurcating stipe, from 2.5 to 3 mm. in width be- 

 tween the bifurcations, and 0.5 mm. in greatest thickness. Bi- 

 furcations frequent, commonly at intervals of about 8 or 9 

 mm. After bifurcation the two divisions bend a little toward 

 each other. Non-poriferous margin narrow. Cell apertures in 

 parallel longitudinal rows between strong elevated ridges; eight 

 or ten rows just before bifurcation, half going into each divi- 

 sion, soon after bifurcation the number of rows reaches by in- 

 terpolation the normal number seven or eight. Those in ad- 

 joining rows alternate with each other, causing an arrangement 

 in intersecting series extending diagonally across the branch. 

 Apertures almost circular or oval, about 0.2 mm. in diameter 

 and six in three mm. measuring lengthwise, those in the margi- 

 nal rows a little larger than the central ones, with a slightly 

 elevated peristome, a little stronger at the outer side, causing the 

 apertures to appear a little oblique. Lunariurn strong only in 

 old examples, usually quite inconspicuous. End spaces equal to 

 about one and a half times the diameter of the cell apertures. 

 Internal structure in accord with generic requirements. 



This seems to be a characteristic species of the western ex- 

 posures of the Hamilton group, if not also of the eastern. It 

 is closely allied to C. sukata (Stictopora sulcata Winchell) but 

 differs in the disposition of its parts. 



Position and locality: Hamilton group. Buffalo, Iowa and 

 Rock Island, 111. The same or a very similar form occurs at 

 Eighteen Mile creek in N. Y., and near Milwaukee, Wis., on the 

 lake shore. 



CYSTODICTYA NITIDA Ulrich. 



PL LXXVI, flg. 4 Ic. 



Zoarium a narrow stipe, about 1.5 to 2 mm. in width, branch- 

 ing dichotomously at intervals of from 8 to 12 mm. Non-po- 

 riferous margin very narrow. Apertures in linear series, between 

 scarcely elevated ridges, five to eight of these series upon each 



