254 PROCEEDINGS OF THE ACADEMY OF 



there, those on opposite sides of this line alternating. Depressions between 

 the costae several times as wide as the costae themselves, but diminishing 

 regularly and gradually in breadth, from tin larger to the smaller extremity 

 of the shell.. 



Length of a specimen incomplete at the larger end, 2-SO inches ; breadth, 

 (as obliquely flattened by pressure), 1*20 inch. Number of costae near the 

 larger end, in - 30 inch, 6; do. in same space, 0*75 inch from the smaller 

 extremity, 12. 



This species presents a marked contrast to the last, in its more widely sepa- 

 rated costae, as well as in having the costae much more finely crenate ; indeed, 

 to the natural eye, they seem to be perfectly smooth. When carefully exam- 

 ined under a magnifier, however, they are seen to be very minutely crenate. 



Locality and position. Waver ley Sandstone, Richfield, Summit County. 

 Ohio, 50 to 60 feet below the Millstone Grit. 



? Genus TENTACULITES, Schlotheim, 1820. 

 Tentaculites tenuistkiatus, M. & W. 



Shell attaining a rather large size, gradually tapering, and a little curved : 

 annulations large, prominent, rather obtuse near the smaller end ; separated 

 by rounded constrictions of about 0*10 inch breadth at the larger extremity 

 of a specimen one inch or more in length. Surface marked by numerous, very 

 fine, regular, closely arranged longitudinal stria?, most distinctly marked in 

 the rounded depressions between the annulations. Aperture circular. 



Length, 1*16 inches ; breadth at the aperture, measuring upon one of the 

 rings, - 25 inch ; do. between the rings, 0*19 inch ; space occupied by four 

 rings and the three intervening spaces at the larger end, 0*30 inch ; while the 

 same space includes six rings at the smaller end. 



This species resembles rather closely the enlarged figure of a form from the 

 same horizon, referred by Prof. Hall to his T. flexuosa, (pi. 78 fig. 26, Palaeont. 

 N. Y. Vol. 1.) ; but its annulations are sharper, and its longitudinal stria? 

 more crowded ; while the natural size #of the New York species is much 

 smaller. 



Dr. Shumardhas also described, under the name T. incurvus, (Missouri Re- 

 port, p. 195,) a similar form, though bis species is much smaller, with more 

 crowded rings, while it also differs in having minute annular striae. 



Locality and position. Cincinnati Group of Lower Silurian Series. Alex- 

 ander County, Illinois. 



Tentaculites Oswegoensis, M. & W. 



Shell attaining a rather large size, very gradually tapering to an acute point, 

 distinctly arched, particularly towards the smaller extremity ; section circu- 

 lar ; annulations rather prominent, somewhat obtuse, from three to three and 

 a half in a space equalling the transverse diameter, diminishing very regular- 

 ly in size, and in their distance apart, from the larger to the smaller extremity. 

 Surface without longitudinal or (visible) transverse stria?. 



Length, 1*45 inches; greatest transverse diameter, 0-16 inch; space occu- 

 pied by six annulations, and five of the intermediate constrictions, at the 

 larger end, 0-35 inch. 



This species has much the general appearance of curved individuals of 7". 

 etongatus, Hall, from the Lower Helderburg Group, (Upper Silurian) of New 

 York, but is decidedly more strongly arched, proportionally more slender, and 

 has more closely arranged annulations, while it shows no traces of the annn- 

 lar" l 8trise seen on the N. Y. species. 



From our T. tenuistriatus, described on the preceding page, it will be dis- 

 tinguished by its more slender form, more closely arranged rings, and the ab- 

 sence of longitudinal striae. The last mentioned character, and its much 



[Dee 



