636 



THE PALEONTOLOGY OF MINNESOTA. 



[LepBrdltella. 



Formation and locaHty. —hower Trenton or Birdseye limestone, Minneapolis, St. Paul and Cannon 

 Falls, Minnesota; Mineral Point, Janesville aiid Beloit, Wisconsin; Kockton and Dixon, Illinois; High 

 Bridge and Frankfort, Kentucky; Lebanon, Lavergne and Murfreesboro, Tennessee; also St. Joseph Island, 

 Lake Huron, and Murray Bay, Canada. It is said to occur in a similar position also in New York. 



Genus LEPERDITELLA, n. gen. 



Leperditia (part.) Uleich, 1892, Amer. Geol., vol. x, pp. 263-268. 



Carapace leperditoid, ovate or oblong, with a straight back; surface of valves 

 without eye tubercle or distinguishable muscle spot, but a more or less obscure broad 

 depression is generally present in the central part of the dorsal half; left valve a 

 little larger than the other, the free edges of the latter fitting into a groove. Length 

 1 to 3 mm. 



Type: Leperditia inflata Ulrich (not L. inflata Murchison sp.). 



Fig. 46'. a, small left valve of Leperditella ivflata Ulrich; 6, inner side of a larger valve of same, show- 

 ing the marginal groove; c, vertical section in outline of entire carapace of same; d, dorsal outline of left 

 valve of same; e and/, externaland internal views of a left valve of Leperditella mundula Ulrich; g and /i, 

 outlines in anterior and ventral views of same; i, right side of an entire carapace of Leperditella cequila- 

 tera Ulrich; j, right valve of Leperditella sulcata Ulrich; k, left valve of L. sulcata var. ventricornis Ulrich. 

 All the figures are magnified 10 diameters, and all the specimens from either the upper or the lower beds 

 of the Birdseye limestone at High Bridge, Kentucky. 



This genus is separated from typical Silurian Leperditia because the left instead 

 of the right valve overlaps the other, and instead of a simple overlap the ventral 

 edge of the right valve fits into a groove in the left. Furthermore, the eye tubercle 

 and muscle spot of Leperditia are not distinguishable externally in Leperditella. In 

 certain Carboniferous species of Leperditia (L. carbonaria Hall, L. nicMesi Ulrich and 

 others) the overlap of the valves, though reversed, is very similar to, that of the 

 - Lower Silurian species here brought together as Leperditella. Perhaps they also 

 ought to be distinguished from Leperditia. 



Leperditella embraces L. tumida, L. mundula, L. cequilatera, L. inflata, L. germana, 

 L. sulcata, and var. ventricornis and L. ? dorsicornis, all described by me in the Amer- 

 ican Geologist for November, 1892, as species of Leperditia. To these I now add L. 

 canalis, L, persimilis and L. macra. With the exception of L. ? dorsicornis, which 

 is from the Hudson River group, all these species occur in strata equivalent to the 

 Birdseye and Black River limestones of New York. 



