BULLETIN NO. 2. 



at both extremities than the dorsal. The surface is covered with 

 round pits which are most numerous and conspicuous near the 

 margins, with traces of delicate longitudinal striae along the cen- 

 ter of the valve when viewed under a good lens. 



Length -j^ inch; height, ^ inch. 



Position and locality : St. Louis limestone, South St. Louis, IMo. 



No. 2497 of the Ilhnois State collection. 



Collector, A. H. Worthen. 



ORDER MOLLUSCA. 



CLASS. CEPHALOPODA. 

 GENUS NAUTILUS, Breynius. 



NAUTILUS M0NTG0MERYENSI8. (sp. nOV.) 



Shell of medium size, sub- globose, volutions two or more, rapidly 

 expanding; outer septum regularly rounded in front and on the 

 sides, wider than long, with a wide and deep sinus in the middle 

 of its dorsal border for the reception of the broad tongue-like 

 projection of the next septum. The succeeding septa are much 

 narrower, and more broadly curved on their dorsal sides, with a 

 long and broad tongue-like projection in • ^e middle that fills the 

 sinus of the preceding septum. Position oi the siphuncle unknown. 

 The specimen is a cast in clay ironstone and shows no surface 

 ornamentation. 



Aperture reniform in shape, and 3 ^ inches in breadth by 1 rf 

 inches in height. Length of the shell from front to back, 3.^ inches. 



Position and locality: Upper Coal Measures, Montgomery 

 county. III. 



No. 2544 of the Illinois State collection. 



Collector unknown. 



GASTEROPODA. 



GENUS PLEUEOTOMABIA, Defrance. 



PLEUROTOMARIA ILLINOIENSIS. (sp. nOV.) 



Shell discoidal, spire but slightly elevated; outer angle of the 

 last volution sharp, volutions about five, aperture ovate. Suture 

 line marked by a row of small nodes, of which about ten may be 

 counted on the last volution. A revolving slightly impressed band 

 may be seen with a good lens above the outer angle' of the last 

 volution, which probably joins the sinus in the hp; umbilicus 

 shallow. 



This shell is most nearly related to the flat variety of P. &pli(eru- 

 lata, described by Prof. Cox, under the name of P. deprcssiis, but 

 differs from that in its more flattened volutions, the impressed 

 band on the lower volution, and its smaller and less conspicuous 

 nodes. 



