New Lower Silurian Bryozoa. 185 



paupera, Ulrich) occupying a higher hoiizon in the shales. R. 

 mutabilis, Ulr., a much larger species, is associated.* 



Position and locality : Lower beds of the Trenton Shales at 

 Minneapolis, Minn., and vicinity. 



RHINIDICTYA HUMILIS, n. Sp. 



Fig. 1U. — Rhinidictya humttis, n. sp. a, two specimens of the natural size, both 

 preserving the basal portion, b. the largest x9, showing the arrangement of the 

 zocecia, granulose interspace^, and frequent bifurcation of the zoarium. 



Zoarium bifoliate, dwarfish; branches strongly convex, 1.0 mm. 

 or a little less in width, arising from a strong basal expansion, and 

 bifurcating at intervals of about 2 mm. Zooecia in from three to 

 five ranges, their apertures impressed subcircular, 0.12 mm. in 

 diameter, widely separated and irregularly arranged over the basal 

 portion, but almost crowded near the distal extremities of the 

 branches. The arrangement of the apertures is either in longitu- 

 dinal rows or in quincunx. When the latter arrangement prevails, 

 seven apertures may be counted in 2 mm., measuring along one 

 of the oblique rows. Interspaces of variable width, more than 

 equal to the diameter of the zocecial apertures on the basal expan- 

 sion, but gradually becoming narrower upward till just beyond the 

 first bifurcation, after which they are subequal and usually about 

 half as wide as the zooecia mouths ; carrying an abundance of 



-The Tennessee species, Bythopora nashvillensis, Miller, which is a bifoliate 

 bryozoan and not a Bythopora at all, but belongs to Rhinidictya, is also related, 

 but is distinguished by its more convex branches, smaller cell apertures and 

 thicker interspaces. 



