G. C. Broadhead — Devonicm of North Missouri. 237 



Art. XXXI. — The Devonian of North Missouri^ with notice 

 of a new fossil y by G. C. Broadhead. 



There is probably not over fifty feet thickness of the 

 Devonian in North Missouri where it is chiefly exposed in the 

 counties of Lincoln, Pike, Ralls and Callaway. In Pike and 

 Ralls the upper portion consists of a few feet of black shales 

 at top with limestone beds below. The fossils contained are 

 chiefly Atrypa retlGularis^ A. aspera^ Sjpirifer eruteines and 

 a few corals. Westwardly in Warren and Montgomery the 

 Devonian is inconspicuous. In Callaway it is better developed 

 and in several neighborhoods fossils are abundant, the most 



prominent being Atryjpa reticularis^ A. affinis^ Gyrtia , 



several species of Strojphodonta^ Orthis iowensis, jStromatopora, 

 Zaphrentis gigantea^ Favosites several species, and several 

 species of Cephalopoda. 



At Providence, Boone County, about 25 feet of Devonian 

 limestone is exposed containing a few rare and interesting fos- 

 sils, including Spirifer eruteines^ Favosites aljpenensis and 

 Stromal ojpor a expansa, and four feet below the top we find 

 Loxonenia robusta^ Murchisonia and an interesting gasteropod 

 not heretofore found in Missouri and not described. The fol- 

 lowing is a description of it. 



Pleurotomaria Providencis. 



Shell subglobose, depressed, spire moderately elevated, apex 

 apparently eroded. Yolutions three or four, the last whorl 

 much expanded. Aperture circular. Surface marked by 

 numerous strise or lines of growth which are occasionally im- 

 bricated, strongly marked and unevenly fasciculated. 



A sulcus one-tenth of an inch' broad and about one-half as 

 deep divides the upper and lower part of each whorl. The 

 striae as they pass from the suture curve backwards, increasing 

 in curvature as they approach the medial sulcus, where they are 

 so much crowded as to form a low border to the sulcus. In 

 crossing the sulcus they are concave in front. On the lower 

 side of the sulcus they also curve backward and form a sharp 

 border to the sulcus similar to that formed above. 



In average-sized specimens there is a row of prominent nodes 

 about half way between the sulcus and the sutare. These 

 nodes at their upper and lower portions are elongated into a 

 low ridge which follows the direction of the lines of growth 

 of the shell, but is soon blended into the body whorl. There 

 is also another range of nodes below the sulcus and some- 



Am. Jour, Sci. — Fourth Series, Vol. II, No. 9. — September, 1896. 

 17 



