Contributions to Invertebrate Paleeontology . 60 



o 



The species is peculiar in its quadrangular form, and in the wide 

 opening through the centre ; in these characters it difiers from any 

 previousl}^ described species. It is of a form that is with difficulty 

 placed in the genus Nautilus — its characters, so far as the external 

 features are concerned, nearly resembling those of Gyroceras — and 

 in the absence of a knowledge of the position of the siph uncle, must 

 remain doubtful. 



Formation and Locality. — In limestone of the Coal Measures, 

 at Canfield, Ohio. Collected by H. C. Bowman, and now in the 

 cabinet of the School of Mines, New York City. 



The following species are forms which characterize two different 

 beds of chert in the Coal Measures in the Hocking "Valley, and are 

 sufficiently pronounced to leave no doubt of their true horizon. 

 These beds have been used as horizons from which to determine 

 the position of the rocks in that vicinity. 



MOLLUSCOIDEA. 



BRACHIOPODA. 



Genus DISCIIVA Lamarck. 



Disciiia Meekaiia Whitf. 



For references and synonym see page 598. 



Specimens of this species are not uncommon in both of these 

 chert beds, the imprints only remaining. 



Genus SPIRIFERA Sowerby. 



Spirifera (Martinia) lineata. 



Plate XVI, figs. 3-5. 

 Spirifera lineata Martin. 



Internal casts, of small size, of this shell are quite common in the 

 upper chert layers of the Coal Measures in Hocking County, bear- 

 ing all the features of the species so far as the casts are concerned, 

 but the matrix was not obtained in a sufficiently perfect condition 

 to yield the external form of the shell. In the black or lower cherts 

 some of the individuals have attained a larger size, one specimen 

 measuring about five-eighths of an inch in transverse diameter. A 

 small individual of the species was obtained in the lower black chert, 



