314 PROCEEDINGS OF THE NATIONAL MUSEUM. vol. xxxv. 



Drepanella. Under the circumstances the writers feel justified in 

 proposing a new genus. with the following brief diagnosis. 



Genus SCOFIELDIA, new. 



Drepanella (part) Ulbich, Geol. and Nat. Hist. Snrv. Minnesota, Final 

 Kept., Ill, Ft. 2, 1894, i>. 670. 



Carapace '2 mm. to 3 mm. in length, oblong, subquadrate, com- 

 pressed; surface of valves broken up into ridges and nodes arranged 

 bilaterally with respect to a small node situated close to the middle 

 of the straight hinge line; on either side a large, irregularly triangu- 

 lar, ridged node, and along the ventral edge a thick, sharply elevated, 

 bar-like ridge. 



Genotype. — Scofieldia hilateralis (Dreparulhi bilaU ralis Ulrich). 



The generic name is given in remembrance of Mr. "Wilbur H. Sco- 

 field, with whom the senior author was pleasantly associated in the 

 study of the Ordovician Gastropoda of Minnesota. 



Genus TREPOSELLA, new. 



Beyrichia (part) Ulrich, Joum. Cincinnati Soc. Xat. Hist.. XIII, 1891, 

 p. 190. 



Carapace small, about 1 mm. in length, semiovate or subquadrate, 

 the hinge long and straight, the other margins curved and supplied 

 with a radially striated frill. Ventral part of valves swollen, the 

 fullness forming a low, not sharply defined longitudinal ridge. Just 

 above this, two unequal nodes, the smaller being of hemispheric form 

 and located just behind the center of the valve. The larger node is 

 somewhat balloon-shaped, situated in front of the middle, connected 

 to the ventral ridge by a narrow neck, from which it extends upward 

 to or slightly beyond the dorsal edge. Between the two nodes, a 

 narrow, sharply excavated sulcus, terminating below in a pit. Fe- 

 male ( ?) provided with a sharply defined, egg-shaped, ventral pouch, 

 located practically midway between the ends. 



Genotype. — Treposella lyoni (Beyrichia lyoni Ulrich). 



This genus is proposed for the reception of what is supposed to be 

 an important link in the evolution of Hollinq from Beyrichia. The 

 female is still provided with a ventral pouch, but it is essentially 

 median in position, while in all true Beyrichia' it is placed well lie- 

 hind the mid-length. The anterior lobe also is essentially as in 

 Beyrichia, but the indefinite ventral swelling is suggestive of Klcs- 

 denia rather than Beyrichia. Compared further with Beyrichia, the 

 cut iiv obsolescence of the posterior ridge of that genus in Treposella 

 i- perhaps the most striking difference. The presence of a sharply 

 defined median pit, as in Eurychilina and other Primitiidse, is prob- 

 ably a reversion to ancestral characteristics. 



