33 



the middle of the body chamber. Section subcircular. Our 

 specimen is somewhat compressed so that a transverse section 

 cannot be accurately determined. The body chamber appears to 

 be bulged on one side. Probably, most tumid on the lower ven- 

 tral side. Our specimen shows six air chambers and probably 

 there were never more than two or three more. If complete, 

 therefore, there would not be more than eight or nine small air 

 chambers. 



When compared with Poterioceres missouriense which this 

 species most resembles, it will be observed, that the body cham- 

 ber is one-half longer, and the septate portion much shorter, in 

 this species, than it is in that one. The inclination of the septa 

 or obliquity toward the tumid side is the same in both species. 



Found by the late Wm. Mc Adams, in the Kinderhook Group, 

 in Jersey county, Illinois, and now in the collection of Wm. F. 

 E. Gurley. 



Family GONIATITIDjE. 



No one has described a Goniaiiie from the Lower or Upper 

 Silurian rocks of America. The species described from the earliest 

 rocks is GoniatUes mithrax, from the Upper Helderberg Group, 

 in Ohio. It is possible that the reference of this species, by the 

 collector, to the Upper Helderberg was erroneous, because rocks 

 of the age of the Hamilton Group, in Ohio, have been frequently 

 referred to the Upper Helderberg, but we think that is not 

 probable, and we have no right to assume such to be the case, 

 without some evidence to support the assumption, and we have 

 none. We only know that many species occur in the Hamilton 

 Group, and this is the only one referred to older rocks. Where 

 are its ancestors or from whence did it come? 



It is a very large species, with four or more volutions. The 

 outer one embraces the inner ones and closes the umbilicus. A 

 transverse section of a volution is semi- elliptical, the dorso- ventral 

 and transverse diameter being about as two to one. 



" The pepta curve gently forward, from the umbilicus for nearly 

 two-thirds of the width of the volution; thence more abruptly 

 backward, forming a broad, low, undefined saddle, to a point 

 nearly three fourths of the width of the volution, when they 

 again bend forward to the margin of the periphery, leaving a 

 broad, deep lobe, which occupies nearly one-third the width of 

 the volution; and thence turning abruptly backward to near the 

 center of the periphery, and sharply recurring, leave an acute 

 triangular saddle on each of the margins, and a narrow, acute, 

 —5 



