634 THE PALEONTOLOGY OE MINNESOTA. 



[Leperdltia fabulites. 



tofore held as belonging to the genus, are now referred to a new genus on the ground 

 that the free edges of their valves are different and the left instead of the right the 

 larger. 



Probably seventy-five good species of the genus are known, the greater number 

 of which and all the larger forms, are restricted to the Lower and Upper Silurian 

 deposits. The earliest forms occur in the Taconic, but it is not till we come to the 

 Trenton that the species become numerous.* The Utica slate and Hudson River 

 group species are nearly all small and of doubtful affinities. The same is true of the 

 Devonian and Carboniferous forms, but in no wise of those which are inclosed in 

 Upper Silurian strata, since in this age the geuus seems to have attained its greatest 

 development both in the way of size and species. 



Leperditia fabulites Conrad. 



PLATE XLIII, FIGS. 10-14 



Cylherina fabulites Conkad, 1843, Proc. Acad. Nat. Sci. Phila., vol. i, p. 332. 



Leperditia fabulites JoNKS, 1856, Ann. Mag. Nat. Hist., 2d .ser., vol. xvli, p. 89; also 1881, idem, 5th sei., 



vol. vlii, p. 342; also 1891, Contri. Can. Micro-Pal., pt. 3, p. 98; Whit- 

 field, 1883, Eep. Geol. Sur. Wis., vol. i, p. 160; Uleich, 1890, Jour. 

 Cin. See. Nat. Hist., vol. xiii, p. 173. 



Leperditia canadensis, yai. josephiana Jones, 1858, Ann. Mag. Nat. Hist., ser. 3, vol. i, p. 341; also 1858, 



Geol. Sur. Can., Dec. 3, p. 94. 



Leperditia fabulites var.j'osepAiana Jones, 1881, Ann. Mag. Nat. Hist., ser. 3, vol. viii, p 344. 



Leperditia josephiana Jones, 1884, Ann. Mag. Nat. Hist., ser. 5, vol. xiy, p. 341. 



Size.— 1. Beloit, Wis., t(E. C.) Length, 12.4 mm.; hight, 7.9 mm.; thickness, 5.0 mm. 



Carapace of medium size, obliquely subovate, comparatively long, widest poste- 

 riorly; ventral curves moderate, strongest just behind the midlength; cardinal line 

 straight, comparing with the length of the valve as 2 is to 3, the two extremities 

 almost equally angular; hight of ends about as 3 is to 4, both obliqely truncate above, 

 the anterior narrowly rounded in the middle; the posterior outline more broadly and 

 evenly curved though having the usual backward swing. Ventral edge of carapace 

 obtuse, scarcely flattened, with a slight furrow on each side near the edge of the 



* Considering that tlie equivalent strata of Kentuolcy, Tennessee and Canada, contains no less tlian eleven species o( 

 Leperditia, it is a little remarljable that only one undoubted species of the genus has so far been discovered In the Trenton 

 series of strata of the northwestern states. 



+ In giving the size of specimens, their condition is indicated by the abbreviations E. O., E. V., and L, V., signifying, 

 respectively, entire carapace, right valve, and left valve. Where these initials are not used, It is to be understood that the 

 dimensions are of an entire carapace. 



