8 Cincinnati Society of Natural History. 



attempt has been made so far to collect any of these species 

 by horizons. 



The following descriptions of fossils are offered as an 

 addition to our present knowledge of Silurian fossils at. three 

 horizons where at present our knowledge is most defective : 

 the Kokomo limestone, the West Union limestone, and the 

 top of the Alger division of the Crab Orchard limestone, 

 which was included in Ohio by Orton under the term Niagara 

 shale. 



Amplexus septatus, sp. nov. 

 Plate I, Figs. 12 A, B. ; Plate II, Figs. 16 A, B, C. 



Corallum simple ; no evidence of gemmation in the speci- 

 mens at hand. Form conico-cylindrical or gently enlarging 

 from the base. The largest specimen found so far has a 

 length of about 60 mm., and a width of approximately 12 'mm. 

 at the top. The exterior is marked by comparatively strong 

 vertical septal ribs of which six to seven, sometimes eight, 

 occupy a width of 10 mm. Transverse striations and moderate 

 annulations or constrictions also present. Transverse tabulae 

 comparativly flat, not deflected at the margins. Radiating 

 septa dififerentiated into primary and secondary septa. Of 

 these the primary septa extend for a distance of about 2 mm. 

 from the exterior surface of the corallum toward the center, 

 in specimens having a diameter of about 10 or 11 mm. The 

 secondary septa frequently do not extend more than three- 

 quarters of a millimeter from the exterior surface. This 

 method of measurement is adopted since the wall of the co- 

 rallum appears more or less thickened by the process of silici- 

 fication in some specimens. Judging from other specimens, 

 the thickness of the wall exceeds a quarter of a millimeter only 

 slightly. The number of primary septa varies from eighteen 

 to twenty-one in specimens about 10 mm. in diameter. There 

 is an equal number of secondary septa. The transverse tabu- 

 lae vary in number from two to four in a length of 3 mm. In 

 some specimens their number may be even less. 



