574" THE PALEONTOLOGY OE MINNESOTA. ^^. ,, 



LWhitella praeolpta. 



.,every essential characteristic of the genus Whitella. We cannot, however, say thig 

 of the specimens which were referred to the species by Hall in 1859 and 1862, and 

 Whithfleld in 1882. since in these cases we are dealing with inequivocal types of 

 Cyrtodonta. The.interior figured by Hall in vol. iii, Pal. N. T., as Palmrca ventrkosa,' 

 is very different from the original Edmondia (now Whitella) ventricosa. That shell 

 seems to belong to the species previously described by Billings as Cyrtodonta suh- 

 carinata. The cast figured by Whitfield, if correctly represented, belongs to a species 

 of Cyrtodonta as yet unknown to me. In his description, however, he included the 

 species which I have named and described on page 537 as Cyrtodonta janesvillennis. 



Comparing W. ventricosa with other species of the genus, W. suhcarinata will be 

 found to have a sharper and more prominent umbonal ridge. In W. rugatina and 

 W. concentrica the anterior end is much larger; W. prmcipta is much narrower poste- 

 riorly and a more elongate shell. 



Formation and locality.— In New York the species occurs in the Trenton limestone at Watertown, 

 Middleville and other locaiijties. If it really occurs in Minnesota, it will be, I think, in the middle 

 Galena of G;Oodhue and Fillmore counties. 



Whitella prmcipta -Ulrich. 



PLATE XLI, FIGS. 15 and 16. 



Whitella prmcipta Ulkioh, 1890. Amer. Geol., vol. vi, p. 386; more fully described and figured in 



1892, Nineteenth Ann. Rep. Geol. and Nat. Hist. Sur. Minn,, p. 246. 



Shell of medium size, ventricpse, very oblique, elongate-ovate or subrhoinboidal 

 in a side view, produced and sharply rounded in the postero-basal region. Beaks of 

 moderate size, prominent, strongly incurved; umbones full; umbonal ridge well 

 ^.marked, traceable almost to the posterior extremity. Anterior end small, short, 

 narrowly rounded; ventral margin gently convex; posterior end produced and 

 narrowly rounded, in the lower part; from the point of greatest extension to the 

 posterior side of the projecting umbones the outline is gently and almost uniformly 

 convex. Hinge line comparatively short, its length less than half the- length of the 

 shell, the edge inflected to form a distinct escutcheon, extending somewhat in front 

 of the beaks. In casts of the interior the internal ligament supports have left 

 distinct impressions of unusual width on each side and behind the impression pro- 

 duced by the escutcheon. An obscurely defined ridge and sulcus is also to be seen 

 running through the middle of the cardinal slope. Anterior muscular scar faint, 

 subovate, acuminate below, situated very near the anterior extremity. Pallial line 

 represented by a thin raised line running parallel- with the margin of the cast. 



This species is very similar to W, obliquata Ulrich, from the upper beds of the 

 Cincinnati group, yet I do not doubt that they are really quite distinct species. 

 That species grows to a larger size, is less elongate, wider posteriorly and with the 



