MISSISSIPPIAN FOSSILS 



103 



GASTROPODA .. Only six genera of Mississippian gastropods 

 are common enough in Ohio to be noted here. No key is necessary 

 as the figures and text will guide the reader to their identification. 



Tropidodiscus is flat-spired, with a characteristic sharp keel 

 on the edge of the whorl which distinguishes it from Euphemites , 

 another flat-spired genus. T. cyrtolites (fig. 262) is common in 

 some beds of the Logan. 



Euphemites resembles Tropidodiscu s in having a flat spire but it lacks 

 the sharp keel present in that genus. Euphemite s 

 nautiloidea (fig. 263) is abundant in the Cuyahoga 

 and another species is rare in the Logan. 



Pleurotomaria t extiligera (fig. 264) has a 

 conical shell of four or five whorls flattened 

 exactly on the line of the slope. The surface is 

 marked by fine axial and spiral ornamentation. 

 Height of a large specimen is a little less than 

 1 1/2 inches. The species is quite common in the 

 Waverly of northern Ohio. 



Mourlonia has a moderately 

 high spire with strong spiral and 

 axial ornamentation. M. 

 stellaeformis (fig. 265) is common 

 in the Logan, along with 2 other 

 species of the same genus. 



Fig. 267 



Fig. 268 



Loxonema is distinguished from the preceding genera by its very high 

 spire and spindle-like outline. L. pikensis (fig. 266) is rare in the Logan 

 except for local concentrations which may contain dozens of specimens 

 closely crowded together. 



The name Platyceras is used here in the wide sense to include loosely 

 coiled shells which vary from almost straight cones to shells in which only 

 the first two whorls are in contact. The cone-shaped forms may be high and almost cylindrical 

 a little distance from the apex or they may be low, flat, and limpet-like. The only common 

 form is P. hertzer i (fig. 267) of the Logan which has a clearly coiled apex. _P. lodiense 

 (fig. 268) is common in northern Ohio. 



Fig. 266 



CEPHALOPODA . Cephalopods are not 

 common in our Mississippian rocks. Both 

 nautiloids and ammonoids occur but the latter are 

 very scarce. Hyde (1953, pp. 336-344) describes 

 and figures 12 species. 



Fig. 269~~ 



The least rare of these is the straight 

 nautiloid Michelinoceras icarus (fig. 269) of the Logan. It is an elongate -conic shell about 

 one inch or less in diameter. 



Prolecanites (fig. 270) is not quite as common as Michelinoceras 

 icarus . It is a coiled ammonoid with a wide umbilicus. Average 

 specimens are about an inch in diameter. Two species occur in the 

 Waverly. 



Fig. 270 



