248 PALEONTOLOGY OF OHIO. 



layers wrap round one another smoothly, without exhibiting any prom- 

 inences, tuberculated surfaces, or mammillations. There are about five 

 lamina in the space of one line; the vertical dissepiments are very slen- 

 der, and often do not pass completely from one laminae to another, and 

 the vesicular compartments or cells open on the surface of each laminse 

 by crowded and very minute rounded or vermicular perforations. 



Position and locality : Corniferous limestone, Kelley's Island, Ohio. 



Steomatopoea sub-steiatella, Mcholson. 



Plate 24, figs. 5, 5a. 



Sarcodeme forming a large sub-spherical mass, composed of very deli- 

 cate concentric layers, of which about ei?ht occupy the space of one line. 

 Vertical dissepiments very slender, often incomj)lete ; about ten to four- 

 teen cells in the space of one line. Surface of the mass smooth, non- 

 tuberculated and non-granulated, without eminences of any kind. The 

 concentric laminse are perforated by exceedingly minute, pin-like, or 

 vermicular perforations, which are arranged so closely as to give to the 

 surface a nebular appearance, and which permit the different strata of 

 cells to communicate With one another. In addition to these very minute 

 openings, the surface shows a number of larger apertures, of a circular 

 form, and varying in diameter from a quarter of a line to half a line, 

 and placed at intervals apart of from two to six lines, though sometimes 

 closer. These openings are not elevated above the general surface, and 

 they are the mouths of canals leading down into the interior of the mass. 

 They are doubtless of the nature of " oscula." 



The specimen from which the above description is taken is a sub-hem- 

 ispheric mass, growing upon a large Brachiopod, and strongly arched 

 above. Its height is about four inches, and its diameter at the base 

 three inches. 



I have some hesitation in separating this form from the Silurian S. stria- 

 tella, D'Orb., of which it may ultimately prove to be only a variety. The 

 lamination of S. striatella, however, is considerably finer — eelven to twelve 

 layers occupying the space of one line — whilst the comparatively large 

 and remote oscula of S. suh- striatella can hardly be supposed to be identi- 

 cal with the tubes described by McCoy (Pal. Foss., p. 13) as travers- 

 ing the laminated tissue of the former species. This eminent palaeon- 

 tologist states that in S. striatella the "upper and under surfaces of 

 slightly weathered specimens " exhibit " vertical vermicular perfora- 



