GASTROPODA. 1043 



Mtclurlnt 



FormaHon atui InomHtf. Maclurea bed of tin- Trenton group. Cute are more or less abundant at 

 in- City auil many other localities In the southern part of the state; Whitewater, 



WUr..n-.in: Dut-n-iii.-, Iowa. 



Cullrfii-n* -Geological and Natural History Survey o( Minnesota; E. O. I'lrlch; W. H. Scofleld. 

 iluteum Register, No. W40, 8441. 



M\<i.ri:iN\ -I-KKOTUKDA Whitfield. 



(Not figured.) 



Maelurta mbrotuifl-i WiiiTKiKi.P. 1*78, Ann. :. Sur. Wli. for l77. p. 7.'.: and I8M, Geol. 



WIs., vol. Iv. p. 246. 



Two <mall cuts, too Imp-rf. .-t f'.r llhistr.it HID. \<-t retaining enough character* tn render tholr 

 !.-.i! IMII with this species aim - -i.iln, were found by Mr. I'lrich In the Maclurea INK! at Stewarl- 

 vllle, Minnesota. Kvidently the species In not far removed from M. cumtata, luit Is a smaller shell, 

 attaining, according to Whltfleld. "a dlanu-U-r of only about one and a half Inches." The casta are 

 proportionally higher than If. tunenta and \\i>- (--nph'-rv much less acute, being almost vertical and 

 rounded belnw where It join- th.- Hal base. At Whitewater, Wisconsin, as In Minnesota, the species Is 

 associated with M. cuntata. 



Family TROUHONEMATID^E, n. fam. 



Shells trochoid, turbiniform or somewhat planorbiform, perforate or im perforate; 

 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 striae; 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 Pleurotomariida- and Euomphalidte, and on the 

 other, through Cychmema, with the Turbinidir. We may say further that the 

 Troclii'/'i. if we admit that the Gotland shells described by Lindst6m as of Trochus 

 are really referable to that family, were derived from Trochonema. Polytrophis, 

 l><'Kouinrk. 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 TrochonematicUf may appropriately follow the Pltur<>lHiarii<l'i ami i'.nm>ij>li,ilid<i 

 and precede the Trochida, Polytroj>lii</'t :md Turbini<l<i. 



Of described genera we place here Trochonema and the perhap- iii'h-tm^ui.-hable 

 l-'.unema of Salter, Cyclonema and the closely related Sir<iph<u>(yltts of Hall, and, with 

 some doubt, Holopea of the same author; also Craspedostoma, Lind-tK-ui. 



