American Palaeozoic Bryozoa. 



245 



Formation and locality: Cincinnati Group. Rather rare near the 

 tops of the hills at Cincinnati, O. 



Prasopora nodosa, n. sp. (Plate XL, figs. 1-16.) 



Zoarium forming small, irregular, or hemispheric masses, from a 

 half inch to one and a half inches in diameter. The lower side is 

 concave, and lined with a wrinkled epitheca, while the upper convex 

 surface is covered by the cell-apertures. 



The cell-bearing surface is covered b^v prominent, closely arranged, 

 but usually unequal monticules; some may be small and conical, 

 others compressed and large, or several may be united, so as to form 

 an irregular node. The ordinary cells have sub-circular apertures, 

 with thin walls, and a diameter varying from y|-g-th to yy^th of an 

 inch (i. e. 11 or 12 may be counted in the space of .1 inch). 

 The orifices of the angular interstitial cells under a low magnifying 

 power are not always readity recognized at the surface. 



As regards internal structure the zoarium is made up of two kinds 

 of tubes, large and small. The large tubes have perfectly distinct, 

 though very thin walls, a diameter of about yyyth of an inch, are oval 

 or Bubcircular in shape, and consequently in contact only at limited 

 points; the interspaces between them are filled by much smaller, and 

 angular interstitial tubes, which apparently are never collected into 

 groups or maculae. The diaphragms of the large tubes are of two 

 kinds, cystoid and straight, and so arranged that the former form a 

 series of convex vesicles on one side of the visceral chamber, while the 

 latter run straight from the preceding to the opposite wall, or, if the 

 cystoid diaphragms are wanting in some parts of a tube, they pass 

 directly across the tube from side to side. The diaphragms of the 

 interstitial tubes are numerous and close set, and are always horizon- 

 tal. A moderate number of small spiniform tubuli may be observed 

 in tangential sections. 



The strongly tuberculated surface, and irregular growth of this 

 species, will distinguish it from all other species of Prasopora known 

 to me. 



Formation and locality-: I collected this species in considerable 

 numbers at Nashville, Tenn., in Saftord's " Orthis Bed," which I regard 

 as being equivalent to the upper beds of the Trenton Group in Ken- 

 tucky. 



DlPLOTRYPA MILLERI, n. Sp. (PI. XI., figS. 2-2c.) 



Zoarium discoid or hemispheric, less than an inch in diameter, the 

 under surface flattened or concave, and covered by a concentrically 



