'656 THE PALEONTOLOGY OF MINNESOTA. 



[Hallielltt. 



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 XLIV, figs. 17 19), but very little to ./. 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, ULRICH, 1890. Jour. Gin. 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. 

 ( ' I'rimitia) seminulum Jones. The Devonian //. retifera, though having something 

 to remind of each, is not a Primitia, lieyrichia, 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 are. I must admit also that I am not thoroughly satisfied that 

 the four species now constituting Halliella are strictly congeneric. They may be so, 

 but until their natural affinities are better understood, the genus is to be accepted 

 as convenient rather than natural. 



HAI,LIEU,A LABIOSA, n. sp. 



PLATE XL VI. Fl<;>. n-40. 



SI/K. -LiTint.il IP. M; nun.: hijrht . O.dU mm.; thickness 0. -10 mm. 



Carapace semielliptical, the, lower three-fourths semicircular, the hinge line 

 nearly straight; dorsal edges somewhat thick and bevelled inward; free edges very 



