656 THE PALEONTOLOGY OF MINNESOTA. 
[Halliella. 
but, as they are only casts of the interior, a narrow border may have existed on the 
exterior of the valves. 
The gibbous character of the anterior part of the dorsal region, and the shortness 
as well as lateral position of the sulcus, are the principal peculiarities of the species. 
In other respects it resembles P. mundula and P. simplex Jones. 
The affinities of this form are rather obscure. There is a suspicious resemblance 
to Jonesella ? obscura (plate xxiv, figs. 17—19), but very little to J. crepidiformis the 
type of that genus. It may also be compared with Placentula inornata Ulrich, a 
Cincinnati species. 
Formation and locality.—Associated with the preceding. 
Genus HALLIELLA, Ulrich. 
Halliella, UuRIcH, 1890. Jour. Cin. Soc. Nat. Hist., vol. xiii, p. 184. 
Similar to Primitia, but with a thicker shell, thick and bevelled edges, and 
usually a larger subcentral sulcus dividing the surface into two lobes. Surface of 
lobes coarsely sculptured or reticulate. 
Types: H. (Primitia?) sculptilis and H. retifera, Ulrich. 
The affinities of this genus are still obscure. Taking H. labiosa, we see Primitian 
characters coupled with those marking Kirkbya, and I am really quite undecided as 
to which are predominant. H. sculptilis Ulrich, from the Trenton of Kentucky, is ~ 
farther removed from Primitia, but its long sulcus produces an effect more like 
Ctenobolbina than Kirkbya. The same is true, though in a lesser degree, of H. 
(Primitia) seminulum Jones. The Devonian H. retifera, though having something 
to remind of each, is not a Primitia, Beyrichia, Ctenobolbina nor a Kirkbya. It is 
these more or less obscure resemblances to a variety of generic types that makes it 
so difficult to point out the diagnostic characters of Halliella, and I find myself in 
the somewhat anomalous position of being much better able to say what they are ~ 
not than what they ave. I must admit also that I am not thoroughly satisfied that. 
the four species now constituting Halliella are strictly congeneric. They may beso, 
but until their natural affinities are better understood, the genus is to be accepted 
as convenient rather than natural. 
HALLIELLA LABIOSA, ”. Sp. 
PLATE XLVI, FIGS. 43—46, 
Size.—Length 0.86 mm.; hight 0.62 mm.; thickness 0.40 mm. 
Carapace semielliptical, the lower three-fourths semicircular, the hinge line 
nearly straight; dorsal edges somewhat thick and bevelled inward; free edges very 
