918 PALEONTOLOGY OF NEW- YORK. 



and the teeth-sockets are large, while the bases of the crura are often 

 distinctly seen. The interior surface is usually papillose. 



Geological formation and localities. This species begins its existence in the 

 Marccllus shale (figure 3) ; and is abundant everywhere in the Hamilton gi'oup, 

 sometimes constituting thin layers to the exclusion of every other fossil. In the 

 eastern part of the State, in the arenaceous shales of this group, it occurs in the 

 form of casts ; and this is its usual condition in Schoharie, Otsego and Madison 

 counties, while from Cayuga lake westward it retains the shell. In some places in 

 Canada West it is found to be the prevailing fossil, while scarcely any other 

 Spirifer occui-s in the same association. I have received specimens of this shell, 

 said to have been found near the Falls of the Maumeo river. It occurs likewise 

 in Maryland and Virginia. 



In the Drift of Ohio, Indiana and Illinois, this species occurs moi-e frequently 

 perhaps than any other fossil. 



The Spirifera bimesialis ( Geol. Report of Iowa, page 507, plate 4, figure 6 ) is 

 closely allied to 8. mua-onata, differing mainly in the much wider area and more 

 elevated beak of the ventral valve. The S. sudattemiata and 8. inutilis of the same 

 volume (pages 504 and 505, plate 4, figures 3 and 4) have similar external cha- 

 racters, with a shorter hinge-line and higher area than 8. bimesialis. These two 

 species are represented in form and proportions (except the extreme naiTow area) 

 by 8. mucronata, Plate 33, figures 19, 20 and 21 of this volume. 



Spirifcra tullla ( n. s.). 



PLATE XXXV. 



Shell gibbous, subelliptical ; length and width about as two to three, or 

 as three to four : hinge-line equalling or greater than the width of 

 the shell ; cardinal extremities truncate or auriculate. 



Ventral valve gibbous, the greatest convexity above the middle of the 

 shell, regularly arcuate from beak to base, curving abruptly to the 

 sides and a little flattened at the cardinal extreraitijs; beak strongly 

 incurved : sinus sharply defined quite to the apex, not deep, rounded 

 in the bottom. Area high, flat in the lower part and extending to the 

 binge-extremities, concave in the upper part. 



