INVERTEBRATES. 495 



It differs, however, in having its anterior end narrower and more pro- 

 duced, with more prominent posterior umboual slopes. ■ 



Locality and position: Galena limestone of the Lower Silurian, in 

 Carroll county, Illinois. 



Ajmbonichia Illinoiensis, Worthen. 



PI. 23, Kg. 4 a, b. 



Shell above the medium size, subovate in outline, not compressed, con- 

 vexity of valves nearly equal, beaks pointed, terminal, slightly oblique 

 and rising above the cardinal margin. Hinge line straight and fully 

 one-half as long as the longer axis of the valves, with which it ranges 

 at an angle of about 35° to 40°. A low ridge commences just below 

 tho beak on the cardinal margin, and gradually widening extends to the 

 base of the shell, and is separated from the umbonal slope by a very 

 shallow depression. Surface of the cast shows twenty or more simple 

 rounded costas separated by narrower interspaces. Other surface char- 

 acters unknown. Greatest length of the valves in the best example 

 seen 3 inches ; breadth at the lower extremity of the hinge line 1.88 

 inch ; convexity of the two valves 1.50 inch. 



Position and locality: Magnesian beds of the Cincinnati Group; 

 Savannah, Carroll county, Illinois. 



GASTEKOPODA. 



GEmxs SUBULITES, Conrad. 



Stjbtjlites inflattis, M. and W. 



PI. 23, Kg. 5. 

 Subidites injlatus, Meek and Wobthen, 1869. Proceed. Philad. Acad. Nat. Sci. 



Shell very ventricose, subfusiform ; volutions about five and a half 

 to six, those of the spire moderately convex in (external?) casts; last 

 one very large, ventricose, and forming much the larger part of the 

 whole, produced and contracted below so as apparently to terminate in 

 a short canal; aperture narrow, rhombic in outline, and pointed or angu- 

 lar above and below; suture well defined in cast; surface unknown. 

 Hightof a specimen with apparently about two whorls at the apex, and 

 a portion of the lower extremity of the produced body whorl broken 

 away, 1.55 inch; breadth of body volution, about 1.15 inch. 



