﻿Cephalopoda of the Cincinnati Group. 



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specimens are attached to the rock so that the one side can hardly be 

 considered as worn away ; others are entirely free and show a remarkable 

 internal structure. 



ii. O. duseri, Hall & Whitfield. 1875. 



Ohio Geol.: Pal. II, 97. PL 3, figs. 2, 3, 4. 



Shell medium size, rapidly enlarging ; section circular; septa concave, 

 gradually enlarging; siphuncle eccentric, nearer centre than margin; sur- 

 face apparently smooth ; edges of septa raised above the general level in form of 

 rings ; on well preserved specimens, the surface is covered with a network 

 of rhombic figures, visible only under the microscope ; along one side of the 

 shell, is a narrow, raised, longitudial line, extending the entire length, but 

 slightly interrupted above each of the rings. 



Locality : Waynesville, Ohio. 



Very well marked by the raised line along the side, interrupted by the 

 septa. The edges of the septa are also raised above the general surface. 

 Only very well preserved specimens show the network on the surface. 



12. O. carleyi, Hall & Whitfield. 1875. 



Ohio Geol.: Pal. II, 98, PL 4, fig. 19. 



Shell with an inner septate tube, gradually tapering ; surrounded by 

 two other tubes, one-eighth inch apart ; septa of inner tube closely arranged ; 

 outer tubes without septa; siphuncle unknown. 



Locality : Fayetteville, Brown county, Ohio ; Covington, Kentucky ; 

 Lebanon, Ohio. 



A most peculiar species. The type specimen is now in the collec- 

 tion of this society. The authors of the species say of it: "The speci- 

 men lies imbeded in the rock, and weathered away to near the centre of 

 its diameter, but the section at the end shows that the inner tubes rest 

 upon, or nearly upon, the inner surfaces of the surrounding ones." p. 99. 



13. O. TENUIFILUM, Hall. 



Ormoceras tenuifilum, Hall, 1847, Pal. of N.Y.I, p. 55, PI. 15, figs. 

 1 a, b, c: 16 figs. 1 a to e : 17 figs. 1 a, b. 



Elongated, sub-cylindrical, gradually tapering to an elongated conical 

 form; siphuncle, ventral, annulated, or expanded into bladder-like rings at the 

 junction of septa; septa moderately concave; surface marked by longi- 

 tudinal, undulated, fine thread-like lines. 



Locality : Cincinnati. 



This species has been placed in Ormoceras and in Actinoceras. It 

 does not seem to differ enough to exclude it from Orthoieras. Its chief 



