362 TWENTIETH REPORT ON THE STATE CABINET. 



GENUS LITUITES (Breyn). 



LITUITES MARSHII ( n. s ). 



PLATE 16 (7), FIGS. 6 & 7. 



Shell of medium size, consisting of three or more closely enrolled volu- 

 tions, which increase in size very gradually from the apex : section 

 circular or subcircular ; slightly flattened on the dorsum, and marked on 

 the sides by sharp, strong, oblique annulations with regularly concave 

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

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

 centre of the dorsum at a point opposite the origin of the second pre- 

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

 making a somewhat abrupt retral curve, become nearly 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 chambers, 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 retral curva- 

 ture on the sides of the volution. Siphuncle small, subcentral. 

 Surface of shell and form of aperture 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 retral 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 the shell. The specimen preserves a little 

 more that two volutions, and we have no portion of the chamber of habi- 

 tation : inferring from the prevailing characters of similar forms of 

 this genus, there has probably been nearly or quite another volution at 

 the apex, which is not preserved. 



Formation and locality. In limestone of the Niagara group, at Kan- 

 kakee, Illinois. 



The specific name is offered as a compliment to Prof. 0. C. Marsh, of 

 New-Haven, whose early labors in paleeontological investigation evince 

 the spirit and dispositions of a gentleman, and an earnest student in 

 science. 



