﻿20 NORWOOD AND PRATTEN ON PRODUCTI. 



P. Buchianus, cle Koninclc. — De Koninck " On the Genus Productus." PI. XVIII., 

 fig. 4. 



Geological Position and Locality. — Found in the black limestone of the coal measures, 

 at Big Creek, Posey county, Indiana. H. Pratten's collection. 



P. ALTERNATUS, 1100. PI. II., fig. 1, «, b, C, d, e. 



Shell of medium size ; length and breadth about the same. In young specimens 

 the dorsal valve is tolerably regularly arched, but is flattened on its anterior part, 

 without showing, however, any anterior prolongment ; when old, it has a decided 

 anterior prolongment, proceeding at right angles from the visceral portion. The old 

 specimens have, also, a wide but shallow sinus. The surface is covered with wide, 

 flattened, transverse bands, placed one above the other, like tiles on a roof. These 

 bands are covered with spines, of which every eighth one reaches from the lower 

 edge of the band above to the lower edge of its own band. Midway between these 

 are other spines, which only reach half way up the band ; and, between these again, 

 are others, which are only half the length of those last mentioned ; and, finally, 

 between the latter come out small tubes or points, which are planted immediately on 

 the lower edge of the band. Some of these tubes are from five to eight millimetres 

 in length, and project downwards close to the shell, forming a fringe around the lower 

 edge of each band. Beak small and passing beyond the cardinal border. Ears small 

 and a little enrolled. 



Ventral valve almost unknown. We have only one specimen which shows any 

 portion of it, and that exhibits only a fraction of the internal surface. It is never- 

 theless, sufficient to show that this valve possessed bands like those of the dorsal 

 valve, that it followed all its movements, and that its visceral disk approached very 

 near to that of the other valve, there not being a distance of four millimetres between 

 them. Its internal surface is pitted with small hollows, corresponding to the tubes 

 of the dorsal valve. 



Dimensions. — Length, 28 millimetres. Comparison. — Length, 100 ; breadth, 100 ; 

 thickness, 0.14. 



Bands. — On an old specimen the whole number of bands are fifteen. At ten mil- 

 limetres from the beak there are three bands in the space of ten millimetres. 



Comparisons and Differences. — This shell differs from the P. punctatus in being 

 smaller : in its broader and more regular bands ; in the arrangement of the spines on 

 the bands; in its flattened anterior prolongment; and, especially, by the close 

 approximation of the two valves. 



Geological Position and Locality. — Found in the mountain limestone, at Rocky run, 

 Hancock county, Illinois. Rare. 



Explanation of the Figures. — PI. II., fig. 1, a. View of the dorsal valve, showing 

 the transverse folds and stripe. 



