﻿NORWOOD AND PRATTEN ON PRODUCTI. 19 



On the ventral valve, the ribs appear to radiate from the beak. In the first part 

 of their course they frequently bifurcate ; afterwards few of them do so. They go 

 on, however, regularly increasing in size, down to the margin ; and are covered with 

 a great number of elongated tubes, lying closely down on the shell. This valve is a 

 little concave, with a slightly raised varix opposite the sinus of the dorsal valve. 



Dimensions. — Length, 28 millimetres. Comparison. — Length, 100 ; breadth, 111 ; 

 thickness, 0.40. 



Ribs. — At twenty millimetres from the beak there are ten in the space of ten mil- 

 limetres. 



Comparison and Differences. — "We know of no Productus that can be confounded 

 with this species. Its flattened and triangular form, the greatest breadth being near 

 the front margin, from which it regularly decreases to the beak, as well as the great 

 number of spines on the ventral valve, will at once distinguish it from all others. 



Geological Position and Locality. — It occurs in nodules of black limestone, imbedded 

 in a coal seam, at Charboniere, Missouri. 



Explanation of the figures. — PL I., fig. 11, a. Dorsal aspect. 



Fig. 11, b. View of the ventral valve. 



Fig. 11, c. Profile view of the same specimen. H. Pratten's collection. 



This species we dedicate to Dr. S. P. Hildreth, of Marietta, Ohio, one of the oldest 

 pioneers of geological science in the "Western States. 



Section VI. 

 PRODUCTI FIMBRIATI. 



P. Leuchtenbergensis, de Koninck. — De Koninck "On the Genus Productus." PL 

 XIV., fig. 3. 



Geological Position and Locality. — In the mountain limestone at Mason's Landing 

 Jersey county, Illinois. Illinois State Collection. 



P. punctatus, Martin sp. — De Koninck "On the Genus Productus." PL XII., 

 fig. 2. 



Geological Position and Locality. — Warsaw, Illinois, in mountain limestone ; twelve 

 miles North West of Richmond, Missouri; near Casey ville, Illinois, in the coal 

 measures. This is a very common fossil in the Western States. Illinois State Col- 

 lection. 



P. fimbriatus, Sowerby. — De Koninck "On the Genus Productus." PL XII., 

 fig. 3. 



Geological Position and Locality. — Near Alton, Illinois, in the mountain limestone ; 

 and at Big Creek, Posey county, Indiana, in the coal measures. Illinois State Col- 

 lection. 



