VOL. 



J'o"] PROCEEDINGS OF T'lE NATIONAL MUSEUM. 271 



Surface marked by seven to nine longitudinal elevated lines on each 

 face. If transverse stria^. existed they have not been, preserved on the 

 cast or the matrix of any specimens in the collection. 



The conditions of preservation are such that the original form can 

 not be definitely determined, and the angle subtended by the sides of 

 the pyramid is unknown. The apparently equal sides indicate a quad- 

 rangular section and a long, narrow pyramid. The specimen illus- 

 trated is the matrix of a crushed shell, showing the depressed line at 

 the angle and the longitudinal lines of the faces. The longest specimen 

 has a total length of G«'" and a width of 16""" on one face at the aper- 

 tural end. 



Formation ami locality. — Middle beds of the Upper Cambrian (Pots- 

 dam) sandstone, Pilot Knob, Wisconsin. Collector, Dr. Cooper Curtice. 



Nut. Mus. Cat. Invert. Foss., 23848. 



Spirodentalium gen. nov. 



Shell tubular, curved, opened at both ends; attenuated posteriorly; 

 aperture circular. 



Surface spirally striated. 



Type: Spirodentalium osceola. 



This genus is founded to include a species that, with the exception 

 of spiral striie, might be referred to the recent genus Dentalium. Tlie 

 presence of spiral striae, and the fiict that it occurs so low down in the 

 Paleozoic, are the principal reasons for distinguishing it from Den- 

 talium, 



Spirodentalium osceola sp. nov. 



Plate XX, Fig. 12. 



Shell elongate tubular, curved, longitudinally marked by several 

 narrow grooves (two only are shown in the cast), open at both (?) ends, 

 and gradually tapering towards the posterior end. Aperature, as far 

 as known, circular and not constricted. Surface ornamented by spiral 

 striai that, from the portion of the surface preserved, passed around 

 the tube three or four times in a length of G centimeters, the tube having 

 a diameter of 7 millimeters at the aperature and 2.5 millimeters at the 

 posterior end. 



The specimen of this species now known occurs in a friable, brown 

 sandstone as cast and the matrix. The drawing was made from a plaster 

 cast taken in the matrix. The circular form of the tube is shown by 

 the interior cast. Whether the posterior end terminates in an opening 

 is not proven positively, but in the only specimen known it ends 

 abruptly where the tube has a diameter of 2.5 millimeters. There is a 

 slight trace of what may have been the tube, 1 centimeter further on, 

 but this is uncertain. 



