CEPHALOPODA— CYRTOCHOANITES. 



129 



179. P. oviforme Hall. (Fig. 1376.) ^ Devonic. 

 Small, short and thick, ovoid, with broadly oval to subcircular 



section; sides of adult portion nearly parallel; final portion of 

 living chamber only contracted into a trilobate aperture ; surface 

 with lamellose growth lines; siphuncle near the ventral side. 

 Agoniatite limestone (Marcellus) of New York. 



180. P. lunatum Hall. (Fig. 1377.) Devonic. 



Fig. 1377. Poterioaras lunatum^ two portions of same shell, X M- (After Grabau, 

 copied from Hall. ) 



Large, regularly arcuate, exogastric ; section broadly oval ; 

 regularly enlarging in earlier portion, but with sides nearly par- 

 allel in adult; aperture slightly contracted; siphuncle moniliform; 

 surface with growth lines and faint longitudinal striae. 



Hamilton of New York. 



181. P. turbiniforme (M. and W.). Devonic. 

 Small, rapidly expanding, slightly asymmetrical, and of nearly 



circular section ; living chamber very short, two or three times as 

 wide as long, rounding to aperture which is transverse, with 

 rounded ends and deep rounded ventral sinus. Siphuncle marginal. 

 Hamilton (Sellersburg) beds of Indiana and Kentucky. 



182. P. minum (Beecher). Devonic. 

 Less abruptly expanding than preceding ; livihg chamber longer ; 



form pear-shaped ; aperture small, trilobate. 



