May, 1919] Silurian Fossils From Ohio 385 



Trochonema fatuum (Hall). 



Plate XVII, Figs. 7 A, B. 

 1868. 20th Rep. New York State Cab. Nat. Hist., p. 345, pi. 15, figs. 7, 8. 



An unknown species of Trochonema occurs in the Holoph- 

 ragma zone, at the top of the upper or Lilley member of the 

 West Union formation, at the Zink or Corporation quarry, 

 within the eastern limits of Hillsboro, Ohio. The general 

 resemblance of the Hillsboro specimens to Trochonema fatuum, 

 from the Racine of Wisconsin, is considerable, although in size 

 they are much smaller. They agree in the following features : 



Characterized by the broadly concave peripheral area extending; 

 longitudinally along the whorls, bounded above and below by an acute 

 and fairly prominent ridge. From the upper ridge to the upper suture 

 of the whorl the slope is gently concave. From the lower ridge toward 

 the umbilicus the curvature is rather evenly convex. 



Diaphorostoma hillsboroensis vSp. nov. 



Plate XVII. Figs. 10 A-D. 



The inner margin of the aperture apparently is thin, as in Diaph- 

 orostoma. vSpecies small, none of the specimens exceeding 16 mm. in 

 diameter. Whorls about four ; the apex of the shell rising but moderately 

 above the outer whorl. The chief characteristic feature consists in the 

 presence of low revolving lines, which vary from 6 in a distance of 

 2 mm. to 9 or 10 in the same distance. These revolving lines often are 

 not conspicuous and are readily overlooked. 



Locality and Position : In the Holophragma zone, at the 

 top of the upper or Lilley member of the West Union formation, 

 within the eastern limits of Hillsboro, Ohio. 



Platyceras angulatum (Hall). 

 Plate XVII, Figs. 2 A, B. 



For somewhat more than one volution the whorls at the apex of 

 the shell are in contact with each other; then they become free for a 

 distance of at least one volution. There is a slight tendency toward 

 longitudinal ribbing, one rib being peripheral in location, a second 

 being basal, and a third following the inner margin of the last whorl, 

 where the umbilicus would be in a closely coiled shell. 



The specimen here figured was found in the Cedarville 

 dolomite in the quarry at Cedarville, Ohio. 



