CORALS AND BRYOZOA. 83 



form appearance ; on the thicker portions of the frond the cells are slightly 

 oblique or at right angles to the surface. Apertures sub-circular, trilobate, 

 diameter .33 mm., margins parallel with the surface; separated from each other 

 by a space equal to or greater than their own diameter ; usually alternating and 

 frequently imbricating. On the thinner part of the frond the anterior portion 

 of the peristome is slightly, and the posterior portion very strongly, elevated ; 

 sometimes having a height of .40 mm. On the thicker portions of the frond 

 the margins are nearly equally elevated. On the posterior margin are two 

 prominent denticulations, which in the course of growth form two parallel 

 striations along the interior of the cell wall. Surface with slightly elevated 

 monticules, the centers of which are distant from each other 5 mm. Inter- 

 apertural space buUate. ' Intercellular space vesiculose. 



Formation and locality. Upper Helderberg group, Falls of the Ohio river. 



Lichen ALIA (Pileotrypa) clivulata. 



I'LATE XXXI, FIGS. 30-3i. 



lAchenalia clinulata. Hall. Trans. Albany Institute, vol. x, abstract, p. 9. 1881. 



" {Pileotrypa) clivulata. Report of State Geologist for 188.5. Expl. pi. 31, tigs. 30-32. 1887. 



ZoARiUM tubular or ramose, hollow. In the specimen described the diameter of 

 the frond is 8 mm., thickness of zoarium about 1 mm. Cells tubular, at right 

 angles to the surface ; without septa. Apertures trilobate, length of opening 

 .15 mm., width two-thirds the length; radiating, closely disposed, not in con- 

 tact. Posterior portion of peristomes strongly elevated, denticulated, pro- 

 jecting over and partially concealing the opening. Monticules rounded, 

 centers distant 2 mm., bases in contact, a small space at the center smooth. 

 The cell apertures radiate from the centers of the monticules, those imme- 

 diately adjacent to them slightly larger than the others. Surface granulose. 

 Intercellular space occupied by septate tubuli. 



This species may be distinguished from L. (P.) denticulata, by the less crowded 

 appearance of the cell apertures, less elevated posterior margin, slighter den- 



