GASTROPODA— PLEUROTOMARIID&. 



627 



XXV. Porcellia Leveille. 

 Widely umbilicated, often large shells, the adult whorls coiling 

 in a single plane as in Bellerophon, and with a dorsal slit and prom- 

 inent band. Inner whorls in a flat spire. Surface ornamented by 

 ribs or nodes. 

 78. P. crassinoda (White and Whit.). (Fig. 846.) Mississippi. 



Fig. 846. Porcellia crassinoda, two views of type specimen 

 St. Louis Acad. Sci. Trans., X.) 



(After Weller, 



Very large, dorsum flatly rounded, very 

 broad, with well-marked narrow median slit 

 band ; dorso-lateral angles coarsely nodose, 

 the nodes dying out towards the umbilicus. 

 Cross-section of whorls subtriangular, sur- 

 face with revolving and transverse lines. 



Kinderhook of Iowa. 



79. P. nodosa Hall. (Fig. 847.) 



Mississippi. 



Smaller, volutions more nearly rounded, 

 nodes sharper and more pronounced. 



Kinderhook of Illinois, Burlington of Illinois and Missouri. 



Fig. 847. Porcellia 

 dosa. (After Keyes. ) 



Family Pleurotomariid^: d'Orbigny. 

 XXVI. Raphistoma Hall. 



Flat-spired, umbilicated shells with close sutures and sharply 

 angular volutions of triangular section, without slit or band, but 

 with a shallow notch in the lip at the outer angle, and with the 

 lines of growth interrupted on the flat surface by a raised line and 

 curving forward on the body of the whorl. Ordovicic. 

 80. R. striatum (Emmons). (Fig. 848, c, d.) Ordovicic. 



