CEPHALOPODA. 123 



Only one fairly complete specimen has been collected but it differs so much from 

 other forms that it is used as the holotype of a new species. Fragments of other speci- 

 mens have been collected. 



Occurrence — Crinoidal bed of the Mineola limestone, Montgomery County. 



Genus Diaphorostoma Fisher 



Diaphorostoma snyderensis n. sp. 



Plate 27, figures 1, 8 and 9. 



Description — Spire generally slightly elevated above the body whorl; usually one 

 and one-half to two and one-half volutions preserved. Young shells indicate the earlier 

 presence of one or two more volutions. The body whorl expands rather rapidly and 

 in an occasional specimen is not in contact with the rest of the shell. Aperture sub- 

 orbicular in outline, inclined about 45 degrees from a vertical plane, with a regular 

 margin. 



Remarks — This is the most abundant gastropod in the Snyder Creek shales. There 

 is little variation among the specimens, the largest being the divergence of the body 

 whorl from the rest of the volutions. The specimens showing this variation most 

 markedly would be classed as Platyceras if they were not associated with the other 

 shells. 



CLASS CEPHALOPODA, 



Subclass Tetrabranchiata 



Order Nautiloidea 



Suborder Orthochoanites 



Family Orthoceratidae 



Genus Orthoceras Breynius 



Orthoceras sp. undet. 



Plate 30, figures 4 and 5 



Only fragments of this species have been collected. By projecting the side lines 

 an angle of about 20 degrees is obtained from the apex. The air chambers are 9 to 

 12 millimeters deep. Two specimens are about 7 centimeters in width. Six segments 

 are preserved in each specimen. A much flattened specimen 13 centimeters in dia- 

 meter probably belongs to the same species. 



Occurrence — Snyder Creek shale, Callaway County. 



Orthoceras sp. undet. 

 Plate 29, figures 1, 2, 3, 5 and 7 



Several fragments of an Orthoceras of nearly circular cross-section and with a 

 very small siphuncle are in our collections. The diameter of the preserved parts is about 

 4 centimeters and of the siphuncle 3 millimeters. Some of the specimens are not cylin- 

 drical but they seem to have been flattened. 



Occurrence — Snyder Creek shale, Callaway County. 



