374 PAL/EONTOLOGY OF ILLINOIS. 



an obscurely beaded appearance in vertical sections, with a 

 diaphragm at the constriction. Acanthopores of moderate or 

 small size usually present. 



Type: T. tuberculosa Hall. Range, Trenton to Niagara. 



NICHOLSONELLA n. gen. Zoaria consisting of irregularly inter- 

 twining flattened branches or fronds, sometimes laminated. Zo- 

 cecia tubular, with a few diaphragms in the "mature" region. 

 Apertures circular, with a faint granose peristome. Interspaces 

 wide, occupied by numerous angular mesopores, that more or 

 less completely isolate the zooecia. Walls of both the zooecia 

 and mesopores thin, and in the mature region traversed longi- 

 tudinally by minute tubuli. The interzocecial spaces are filled 

 with a calcareous deposit, into which the minute tubuli con- 

 tinue, but in which the mesopore walls become unrecognizable. 

 Mesopores with rather thick and numerous diaphragms. 



Type: N. pondurosa n. sp. Range, Trenton and Cincinnati. 



CONSTELLARIA Dana. Subramose or frondescent zoaria. Sur- 

 face with stellate maculae, the spaces between the rays more or 

 less elevated and occupied by .two or three short rows or clus- 

 ters of closely approximated zocecial apertures. Zooecia with 

 rather thin walls, small, circular apertures and peristome, 

 equally distributed and partly in contact with each other in 

 the spaces between the stellate maculae. Mesopores abundant, 

 aggregated in the maculae, always closed at the surface, with 

 gradually crowding horizontal diaphragms. Zooecial tubes with 

 few or moderately numerous diaphragms. True acanthopores 

 wanting. 



Type: C. florida, Ulr. Range, Trenton to Cincinnati. 



STELLIPORA Hall. Zoaria forming thin crusts over foreign 

 bodies. The upper surface exhibiting at rather irregular inter- 

 vals stellate monticules. Zooecia with sub-circular apertures 

 occupying only the summits of the radially arranged short 

 ridges, the depressed central space and furrows between the 

 ridges, as well as the intermacular spaces, appearing non-cellu- 

 liferous at the surface. Thin sections, however, show them to 

 have been occupied by rather small, angular mesopores, which 

 are more closely tabulated than the zooecial tubes, and like 

 them arise from the epithecal membrane. 



