FOSSILS OF THE SILURIAN AND DEVONIAN ROOKS. 195 



examine other internal features. The outside appearance of the shell offers 

 few points for description which the illustration does not plainly show. 



Formation and Locality. Found in the Corniferous limestone of the Devonian formation, at and 

 around the Falls of the Ohio, in Kentucky and Indiana. 



Genus Lituites. 



Etymology : leiuus, a trumpet. 



Lituites marshi. HALF.. 



Plate XXX., figure 1. 

 Liiuiiea marshi , Hall. 20th Regent's Rep., p. 3621867. 



Shell of medium size, consisting of four or more closely enrolled volutions, 

 which increase in size gradually, but very slowly, from the apex ; transverse 

 or cross-section circular or sub-circular ; slightly flattened on the dorsum, and 

 marked on the sides by sharp, strong, oblique annulations, with regularly con 

 cave spaces between them. These ridges, rising on the ventral margin, are 

 directed obliquely backward as they cross the sides of the volutions, reaching 

 the center of the dorsum at a point opposite the origin of the second preceding 

 one, having their greatest elevation on the sides of the shell, and maJdng a 

 somewhat abrupt retrorse curve, become almost obsolete on the dorsum. Septa 

 moderately distant, deeply and regularly concave, the chambers regularly 

 increasing in depth with the diameter of the shell. The space of three cham- 

 bers, measured on the side of the shell, are equal to the dorso-ventral diameter 

 of the volution. The dorsal margins of the septa are directed forward, giving 

 a broad rectral curvature on the side of the volution. Siphuncle small and 

 sub-central. 



Surface of shell and form of aperture are unknown. This beautiful species 

 is readily distinguished by its slender volutions, and the strong, oblique ridges, 

 which, in the outer part of the shell, are a little more distant than the septa, 

 while on the inner volutions they are nearer to each other, the increase in the 

 distance of the annulations being a little more rapid than that of the septa. 

 Owing to the retrorse curving of the annulations, and the advancing curvature 

 of the septa, the ridges are cut by the latter near the dorso-lateral angle of the 

 volution, throughout the greater part of the extent of shell. 



In the specimen illustrated on plate 30, both termini of the shell are missing ; 

 it has preserved more than three complete volutions. The vacant central space 

 indicates that, probably, two full volutions are obliterated there at the apex. 

 How much there is destroyed at the other end can not be ascertained, but that 



