420 GEOLOGY OF OHIO. 



original labsl, and I have seen several specimens of the species from the 

 same formation. R. dactyloides (Dictyocrinus dactyloides Conrad) is also 

 from about the same horizon. Both of these species, however, are in 

 the Silurian, while the present species brings the genus up to the Devon- 

 ian ; so that we now know of its existence from the base uf the Lower 

 Silurian to the Lower Devonian. 



RADIATA. 

 Genus STYLASTREA Lonsdale. 



Stylastrea Anna. 



Plate II, figs. 1-5. 

 Stylastrea Anna x Whitf., Ann. N. Y. Acad. Sci., March, 1882, p. 199. 



Corallum compound, growing in irregular or more or less hemispherical 

 masses of several inches in diameter, which are formed of a large number of 

 closely aggregated polygonal cell-tubes or polyps, of rather small size, divided by 

 intercellular walls of considerable thickness, as in most forms of the compound 

 Cyathoph-v Hides. Full-grown polyps, measuring about half an inch in diameter, 

 but usually somewhat smaller ; the prevailing size being about three-eighths of an 

 inch. Calyces deep, abruptly declining from the intercellular walls to a, depth 

 nearly equaling the tranverse diameter. Longitudinal septa or rays well developed, 

 extending about one-third, or less of the diameter of the tube from the outer wall, 

 and averaging about forty in number in adult individuals; some containing thirty- 

 six, and one large one counted gives forty-two. Crest of the rays strongly denticu- 

 late, the denticles being thickened and knot-like at their junction with the rays. 

 Central chamber within the limits of the longitudinal rays, equal to one-third of 

 the entire diameter of the polyp, and divided by numerous distinct . transverse 

 tabulae, which are variously bent or interrupted by contact with the adjoining ones, 

 leaving irregular cavities of considerable size between them. Interseptal spaces 

 ocrupied by a series of horizontal plates, which originate at the outer wall, and 

 extend upward and inward with increased growth to the edge of the rays, where 

 they form the denticulation of the crest. Between the latter plates, the spaces are 

 occupied by the smaller irregular vesicular structure. 



The species, in its general features, resembles Cyathophyllum rugosum 

 Hall, sp., from this formation, and may be easily mistaken for that one, 

 in obscure or imperfect specimens; but where the internal structure is 

 observable, especially in longitudinal sections of the polyps, can be very 

 readily distinguished by the large central space in each polyp, and by 

 the strongly developed transverse tabulae; also by the rays not extending 

 to the centre, as in that species and in those of the genus Acervularia. 

 When the coral is weathered, or the substance becomes chalky, so that 

 the polyps are readily separable from each other longitudinally, the 

 appearance very closely resembles that of Cyathophyllum rugosum when 

 in a similar condition, but the interruption of the rays before reaching 

 the centre, arid the great extent of the tabulae, will then serve to distin- 

 guish them. 



Formation and Locality. — In the Upper Helderberg group, in Pauld- 

 ing county, Ohio. 



'Named in honor of Mrs. Orton, wife of President Edward Orton, of the State 

 University, Columbus, Ohio. 



