520 Contrihuiioiis to Invertebrate Palseontology. 



Rensselaer rol3'technic Institute, bearing the original label, and I 

 have seen several specimens of the species from the same formation. 

 a. dactyloides {Dictyocriniis dactyloides Conrad) is also from about 

 the same horizon. Both of these species, however, are in the Silu- 

 rian, while the present species brings the genus up to the Devonian ; 

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

 Silurian to the Lower Devonian. 



RADIATA. 



Genus STYLASTREA Lonsdale. 



Stylastrea Anna. 



Plate VI, tigs. 1-5. 



Stylostrea Anna'^ 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 com- 

 pound Cyathoplujll'uhc. Full-grown polyps, measuring abortt 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 inter- 

 cellular walls to a depth nearly equalling the transverse diameter. Longitu- 

 dinal septa or rays well developed, extending about one-tliird, 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 denticulate, 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 tabulse, 

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

 leaving irregular cavities of considerable size between them. Interseptal spaces 

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

 ana extend upward and inward with increased growtli 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 Cyallwphyllum 

 rugoxiim Hall, sp., from this formation, and may be easily mistaken 

 for that one, in obscure or imperfect specimens; but wlu're the 

 internal structure is observable, especially in longitudinal sections 

 of the polyps, can be very readily distinguished by the large central 



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

 State University, Columbus, Ohio. 



