GASTROPODA. 1043 
Maclurina subrotunda.] 
Formation and locality.—Maclurea bed of the Trenton group. Casts are more or less abundant at 
Wykoff, Stewartville, Lime City and many other localities in the southern part of the state; Whitewater, 
Wisconsin; Dubuque, Iowa. 
Collections.—Geological and Natural History Survey of Minnesota; BE. O. Ulrich; W. H. Scofield. 
Museum Register, No. 8440, 8441. 
“Macturina susrorunpa Whitfield. 
(Not figured.) 
Maclurea subrotunda WHITFIELD, 1878, Ann. Rep. Geol. Sur. Wis. for 1877, p. 75; and 1882, Geol. 
Wis., vol. iv, p. 246. 
Two small casts, too imperfect for illustration, yet retaining enough characters to render their 
identification with this species almost certain, were found by Mr. Ulrich in the Maclurea bed at Stewart- 
ville, Minnesota. Evidently the species is not far removed from M. cuneata, but is a smaller shell, 
attaining, according to Whitfield, ‘‘a diameter of only about one and a half inches.” The casts are 
proportionally higher than M. cuneata and the periphery much less acute, being almost vertical and 
rounded below where it joins the flat base. At Whitewater, Wisconsin, as in Minnesota, the species is 
associated with J cuneata. 
Family TROCHONEMATID A, n. fam. 
Shells trochoid, turbiniform or somewhat planorbiform, perforate or imperforate; 
margin of aperture entire, simple, rarely trumpet-shaped, sometimes with a wide 
angled notch and carina in the upper or outer part; no slit nor distinguishable band; 
surface with several strong revolving ridges or more numerous spiral strie; test 
very slightly or not at all nacreous. Operculum unknown, probably incapable of 
preservation. 
While it is impossible at the present time to give a fair estimate of the probable 
limits of this family, we may yet say with confidence that it is connected on the one 
hand through Trochonema with the Pleurotomariide and Euomphalide, and on the 
other, through Cyclonema, with the Turbinide. We may say further that the 
Trochide, if we admit that the Gotland shells described by Lindstém as of Trochus 
are really referable to that family, were derived from Trochonema. Polytrophis, 
DeKoninck, which because of its remarkable operculum deserves to rank as a 
separate family, also most probably was derived from certain members of the same 
genus. But as we will refer to these alliances in greater detail in our remarks on 
Trochonema and Cyclonema, it may suffice to say that to the best of our knowledge 
the T’rochonematide may appropriately follow the Pleurotomariide and Euomphalide 
and precede the T'rochide, Polytrophide and Turbinide. 
Of described genera we place here Trochonema and the perhaps indistinguishable 
Eunema of Salter, Cyclonema and the closely related Strophostylus of Hall, and, with 
some doubt, Holopea of the same author; also Craspedostoma, Lindstiém. Besides 
