404 PALEONTOLOGY OF ILLINOIS. 



with a depressed delicate calcareous plate, that closes a little 

 less than two-thirds of the opening, the orifice left being sub- 

 triangular in form, without thickened margins, and situated at 

 the anterior side. With age, a second, third and more layers 

 of zooecia are developed directly over the first, so that they 

 gradually form a zocscial tube seemingly having the cavity in- 

 tersected by incomplete diaphragms. These appear to spring 

 from the posterior wall and extend about one-half the distance 

 across. 



Type and only known species: Cyclopora discoideti Prout. 

 Keokuk group. 



? CYCLOPOKELLA n. gen. Zoarium a thin discoidal expansion. 

 Zooecia sub-tubular, with a succession of superior hemisepta in 

 the vestibular portion. Irregular mesopores abundant. Acan- 

 thopores of large size, numerous. 



Type: C. spiinfera Ulrich. Keokuk group. 



Family HELIOTKYPID.E Ulrich (Provisional.) 



HELIOTRYPA IJlrich. Zoarium bifoliate. Primitive portion of 

 zooecia sub-tubular, thin-walled and prostrate upon the median 

 laminae. Superior hemiseptum moderately developed. Vestibu- 

 lar or outer portion of the zooecia thick-walled, the walls tra- 

 versed obliquely by radially arranged minute tubuli. Inter- 

 spaces of variable width, occupied by numerous, irregular, 

 rounded, thick-walled and tabulated mesopores, which are also 

 aggregated at intervals to form maculae. Walls of mesopores 

 and zooecia vestibules amalgamated. Median tubuli present be- 

 tween the median laminae. Superficial apertures circular, sur- 

 rounded by a sloping area. Interspaces flat between the meso- 

 pore apertures. 



Type and only known species-: H. bi folia Ulrich. Chester 

 group. 



