INVERTEBRATES. 531 



Carbonarca gibbosa, M. and W. 



PI. 33, Fig. 0. 

 Carbonarca gibbosa, Meek and Worthex, 1876. Proceed. Acad. Nat. Sci., Phila., p. 40. 



Shell transverse, short-oblong, very convex ; posterior side wider than 

 the other, and vertically subtruncated; anterior margin rather narrowly 

 rounded; ventral margin nearly straight along the middle, but sloping 

 and rounded up anteriorly, and more abruptly behind, cardinal edge 

 equaling two-thirds of the whole length ; larger anterior teeth inclined 

 forward and upward, and those of the small series ranging nearly verti- 

 cally, or slightly inclined forward anteriorly, and a little backward 

 behind; umbones gibbous, but with their outer and upper surfaces a 

 little flattened, so as to impart a slightly subangular or prominent char- 

 acter to the post-umbonal slopes ; immediate apices of the strongly 

 inclined beaks placed about one-fourth the entire length of the shell 

 behind the anterior extremity. Surface markings unknown. 



Length 0.82 inch ; hight to top of cardinal margin (of cast) behind 

 the beaks 0.56 inch ; hight to top of the umbones 0.65; convexity of the 

 two valves 0.57 inch. 



Position and locality : Springfield and LaSalle, Illinois, Upper Coal 

 Measures. The specimens from the latter locality are, in some exam- 

 ples, more depressed and oblique than the typical form from near 

 Springfield, and these may possibly belong to a distinct species, if the 

 differences noted are not due to accidental distortion. If really distinct, 

 this form might be called O. depressa. 



Genus NAUTILUS, Linnaeus. 



Nautilus (Discites) Highlandensis, Worthen. 



PI. 33, Fig. 2. 



Shell of medium size, discoid, compressed; whorls about three, con- 

 tiguous, nearly fiat on the sides, the greatest convexity being near the 

 inner margin, which is gently rounded. Septa rather closely arranged, 

 crossing the sides with a graceful backward curve, and also curving 

 backward on the narrow truncated periphery. Last or body chamber 

 long and proportionally broadj forming about half the outer volution. 

 Surface markings and siphuncle unknown. 



This shell in general form resembles Nautilus (Discites) disciformis, 

 M. and W., from the Keokuk limestone, but differs from that in its 

 much smaller size, (none of the specimens seen attaining a diameter of 

 more than 3.50 inches,) and by its proportionally broader outer chamber. 



Position and locality : LaSalle, Illinois, and near Highland, in Madi- 

 son county, where it is found in the Shoal creek limestone above coal 

 No. 9. I am indebted to Mr. Ad. F. Bandelier, of Highland, for the 

 use of the example figured. 



