88 Cincinnati Society of Natural History. 



MANUAL OF THE PALKOXTOLOOV OF THK 

 CINCINNATI GROUP. 



By Joski'H F. Jamks, M. Sc, F. G. vS. A. 

 Part III. 



(Continued from Vol. xiv, p. 163.) 



(Read l)y Title June 7, 1S92.) 



Sub-class vStk()MATop()K()I1)i:.\. 



A group of Hydrozoa, with a calcareous and frequently 

 large-sized " coenosteum " or skeleton ; varying in form from a 

 spherical or irregular and sometimes branched mass, to a thin, 

 flattened expansion ; frequently attached to some foreign body 

 by a single point, or by an epithecal membrane ; exhibiting, 

 more or less clearly, a series of concentric laminx, separated 

 by interlaminar spaces ; the former arising from processes 

 given off at certain definite points from rods or pillars running, 

 either between two lamina;, or crossing several in succession ; 

 outer surface with numerous minute pores, or obtuse, imper- 

 forate projections. 



The group is confined to Silurian and Devonian rocks, and 

 is made by Nicholson to include the aberrant Dcatricea, as 

 well as the typical Stroniatopora, (Man. of Pal., vol. i, 1889, 

 pp. 229-231). In the Cincinnati Group three genera are 

 represented, the characters of which arc given below. 



Genus i. — Stromatoi'ORA, Goklfu.ss, 1S26. 



Skeleton (ccenosteum) consisting of concentric, calcareous 

 lamince, separated by distinct interlaminar spaces, which are 

 cros.sed by numerous radial pillars; radiating water canals 

 and surface grooves sometimes present, and placed around 

 minor centers: openings of large canals (o.scula) al.so some- 

 times ])resent ; growing in irregular masses, sometimes with 



