i8o Natural History Bulletin. 



pressed, but little elevated above the outer volution ; umbilicus 

 deep, exposing less than half of each successive volution ; volu- 

 tions four, the last enlarging rapidly, sub-pentagonal in trans- 

 verse section; periphery carinated; a second carina on middle 

 of dorsal side, and a third, less sharp than others, on middle 

 of ventral side of each volution ; volutions flat between periph- 

 eral carincC and the median dorsal and ventral carinas, some- 

 times even concave between periphery and middle of upper 

 side; distinctly concave above between median carina and 

 suture; lower side of volutions rounded between median 

 carina and umbilicus. Aperture sub-penlangular. 



Surface marked by transverse lines of growth crossed by 

 faint revolving strias. 



Associated with ^S". bicarinatiis in Niagara limestone at 

 Monmouth, Iowa. 



BUCANIA, Hall. 



BUCANIA PERORNATA, N. S. 



PLATE III., FIGS. 3 a, b. 



Shell large; two and three eighths inches in length; volutions 

 symmetrical, in same plane, transversely flattened and ellip- 

 tical in cross section except toward the aperture, four in 

 number, partly embracing but all showing in the deep umbil- 

 icus on either side, expanding slowly at first, then abruptly 

 toward the mouth, which is longitudinally elliptical with a 

 diameter equalling two thirds the entire length of the shell; 

 dorsal surface rounded; margin of umbilicus marked in the 

 earlier volutions by a sub-angular ridge which disappears 

 toward the aperture; middle of dorsum marked by a low re- 

 volving ridge bounded on either side by a shallow groove; 

 the rest of the surface ornamented by low ridges beginning 

 on either side at the dorsal groove and running obliquely out- 

 ward and forward over the lateral margin to the umbilicus, 

 and crossed nearly at right angles by another system of more 

 closely set ridges that, beginning in the umbihcus, run out 

 over the lateral margin, and thence over the dorsal surface in 



