636 



'J PALEONTOLOGY OF MINNESOTA. 



[Leperditella. 



Pur mat ion and locality. Lower Trenton or Birdscye limestone, Minneapolis, St. Paul and Cannon 

 Falls. Minnesota; Mineral Point, Janesville and Beloit, Wisconsin; Rockton and Dixon, Illinois; High 

 Bridge and Frankfort, Kentucky: Lebanon, La vergne 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, u. gen. 



Leperdilia (part.) Uuucii, 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, inflata Ulrich; l>, 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/, external and internal views of a left valve of Leperditella, mundula Ulrich: ij and h, 

 outlines in anterior and ventral views of same; t, right side ol an entire carapace of LepcrdilcUn asqwla- 

 I Iricli:./', right valve of Leperditella sulcnta Ulrich; k, left valve of L. aulcuta 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. 



Tliis genus is separated from typical Silurian Leperdttia 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 Leperdttia are not distinguishable externally in Leperditella. In 

 certain Carboniferous species of Leperditia (L. carbonaria Hall, L. nicklcsi 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. tumidn, L. mundula, L. ceqitifatera, L. inflata, L.germana, 

 /.. .-/</<///, i, and vat. i-cntricornis and L. ? dorsicorn is, all described by me in the Amer- 

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

 rnniiHx, L. jirrxiHiilix and L. infirm. With the exception of L. ? dorsicornis, which 

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

 Birdseye and I .lack Hiver limestones of New York. 



