﻿NORWOOD AND PRATTEN ON PRODUCTI. 9 



Section II. 

 PRODUCTI UNDATI. 



P. undiferus, de Koninclc. — " Fossils of Belgium." PI. V., fig. 4, and PI. XL, fig. 5. 



Geological Position and Localities. — In Belgium this shell belongs to the mountain 

 limestone series, while in this country we have found it only in the coal measures, 

 and as yet at only three localities, Casey ville, Illinois, and two places in Posey county, 

 Indiana. At Caseyville it occurs in a thick bed of limestone, overlying the five foot 

 seam of coal. Illinois State Collection. 



P. Rogersii. — nob. PI. I., fig. 3, a, b, c. 



Shell of medium size ; slightly transverse ; dorsal valve very high and strongly 

 enrolled on itself; cardinal border equal to about four fifths of its greatest transverse 

 diameter ; beak rather large, and passing beyond the cardinal border ; ears but little 

 distinct from the dorsal vault. The anterior part is flattened, and possesses a slight 

 sinus. The surface is covered with ribs, of which twelve may be counted in the space 

 of ten millimetres, at the distance of ten millimetres from the beak. It is also 

 covered in its whole extent with transverse folds. Those nearest the beak are rather 

 small, but, after passing the visceral disk they rapidly increase in size to near the middle 

 of the shell, after which they again decrease in size to the margin. The whole anterior 

 portion of the shell seems to have been pretty thickly covered with tubercles, especially 

 between the transverse bands, while a few were distributed over the remainder of the 

 surface. On the middle part of the shell there are only — transverse bands in the 

 space of ten millimetres. 



Dimensions. — Length, 21 millimetres ; breadth, 24 millimetres. 



Comparisons and Differences. — Although we have only one specimen of this species, 

 and from this one the shell is abraded over the greater portion of its surface, still its 

 form and characteristics are so distinct that it cannot be confounded with any other. 

 The P. undatus comes nearest to it, but our species differs from the undatus in having 

 larger ribs, and flattened transverse bands, while the bands of the undatus are sharp. 

 The P. Rogersii is further distinguished by having its anterior prolongment covered with 

 tubercles, some of which, judging from a few remaining fragments, must have been 

 of considerable length. Ventral valve unknown. 



Geological Position and Locality. — This specimen was found by Mr. Pratten in the 

 coal measures, near Huntsville, Missouri, It occurs in a bed of ferruginous limestone 

 overlying a stratum of bituminous shale. 



Explanation of the Figures. — PI. I., fig. 3, a. View of the dorsal valve. H. 

 Prat ten's collection. 



Fig. 3, b. View of the beak, showing at the same time the depth of the sinus. 



Fig. 3, c. The same specimen shown in profile. 



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