CORALS AND BRYOZOA. 
145 
On the celluliferous face the dissepiments are angular, on a plane with the 
branches. Fenestrules of about the same appearance as on the opposite face. 
Cell apertures in two ranges, opening directly outward, disposed around the 
fenestrules, there being two apertures on each dissepiment, seven or eight 
apertures around each fenestrule: margins distinctly elevated but not in¬ 
denting the borders of the fenestrule. Branches and dissepiments carinated, 
connected, carina about .50 mm. in height, at first very thin, but immediately 
expanding and giving an appearance very similar to the non-celluliferous 
face of the frond; carinae of branches about .30 mm. in width, gently en¬ 
larging before bifurcation, angular, slightly carinated; dissepiments .45 mm. 
wide, angular, slightly carinated, on a plane with the branches; interstices 
broadly oval. This surface, if seen from above, would be very easily mis¬ 
taken for the non-celluliferous face of some frond. 
This species very nearly resembles F. (L.) perforata of the Hamilton group, 
but the frond is coarser, the fenestrules larger, the dissepiments less frequent; 
there being only two in the same space occupied by three or four in that species. 
Formation and locality. Upper Helderberg group, Walpole, Ontario, Canada. 
Forms having the carinae connected by scalae which meet midway between the carinae 
of adjacent branches, forming a pseudo-carina. 
HEMITRYPA, Phillips. 1841. 
Fenestella (Hemitrypa) cribrosa. 
NOT FIGURED. 
Fenestella (Hemitrypa,) cribrosa, Hall. Trans. Albany Institute, vol. x, abstract, p, 35. 1881. 
Bryozoum infundibuliform. Branches slender, width above a bifurcation .30 
mm., increasing to .50 mm., more or less rapidly expanding, arising from a 
thin, broadly spreading, striated base, incrusting other objects. The pedicel 
is of uniform appearance and characteristic, usually having a length of about 
5 mm., and a nearly constant diameter of a little more than 2 mm.; the 
branches extend its entire length, and when well preserved they are 
generally rounded, but sometimes angular, frequently concave below a bifur¬ 
cation, with numerous small, elongate, narrow nodes, which are sometimes 
