GASTROPODA. 



<>jrr 



up|-r slope, of which the um.-r third Is alniont horizontal and tin- ut-i two-thirds a strongly concave 

 a sharp a'nul.- or n.i k '.- .hM.llnu the two part*; Mcood, the peripheral band, which Is nearly vertical, 

 margined on each side by a sharp carloa and rendered somewhat bl-concave by a smaller carlna, which 

 first make* Its appearance on the fifth whorl, lying slightly beneath the middle of the space; and third 

 the basal part of the whorl Is flattened rather than ventrloose and traversed by five or six small revolving 

 ridge* and furrows, the last of which mark* off the boundary of the small umbilical perforation. Surface 

 showing !. tine and rather regular lln<* of growth which cross the whorls from above somewhat 

 i.t>li<iu*ly backward. On one beautifully preserved example the whole surface, when highly magnified, Is 

 Men to be covered with a crowded Mt of extremely delicate revolving lines. Aperture subovate or some- 

 what hexagonal. Its hlght slightly exceeding the width; perltreme thin, the Inner Up reflected partly over 

 the umbilicus. 



and loeoUfy. Ctenodonta bed of the shale* of the Klack River group. Minneapolis, Chat- 

 (li-lil and near Cannon falls, Minnesota; also In the limestones of this group In Mercer county, Kentucky. 



CWUeHotu. Geological and Natural History Survey of Minnesota; R.O. Ulrlch. 

 Mutmm Rtgitter, No. 6864. 



(iY RON EM A HEMIOARINATUM Sailer. 

 PLATE LXXVIII. riOS. IT and IS. 



CVdoMSM smieoriiMUa SALTKK, 1889, Can. Org. Eem., Dec. I, p. 27, pi. vi, flgs. 2 and 2a, not 26. 



This species I* distinguished from G. puleMlum by Its stronger lines of growth, and the much 

 greater prominence of the carlna which corresponds with the upper boundary of the vertical peripheral 

 band In that species. The lower boundary Is only very slightly more prominent than the rest of the six 

 or seven revolving carlna- which lie beneath the principal keel. The upper slope of the whorls also Is 

 somewhat wider than In O. pulduUum, and, furthermore, may be, as In the specimen figured, divided 

 on the last whorl by an extra small median carina. This extra carina Is probably not of much conse- 

 quence since It occurs only on a part of the last whorl In our specimen, and Is neither mentioned nor Illus- 

 trated by Salter. 



We have not the least doubt concerning the specific Identity of the Minnesota specimen and the 

 bell represented by Sailer's figures 2 and 2n (toe, cit.), but we cannot say as much for his fig. 26. The last 

 might pass very nell for our O. pulcheUwn since It gives the peripheral band as nearly vertical, the carina 

 which forms lu lower boundary being nearly or quite an prominent as the upper. The upper slope, how- 

 ever, Is not as concave a* It should be In our specie*. 



formation and locality. Phylloportna bed of the shales of the Black Elver group, near Cannon Falls 

 Minnesota. 



OU0ci*m.-K. O. Ulrlch. 



GYRONEMA DUPLICATUM, n. sp. 



PLATE I.XXVIIl. FIOS. 0-. 



Oornp. Pitwotomanapfreannala HALL, 1847, Pal. N. Y., vol. I, p. 177. pi. xxxviu, flg. 4. 



This Is distinguished from G. p-WWfcm, which It resembles In a general way much more closely 

 than It doea O. tmlearinmttim Salter up., by Its larger size, entirely closed umbilicus, and leas angular 

 whorls. The carina on the upper slope of the whorls Is less prominent and smaller (In caste of the Interior 

 t looks more like a thick swelling than a carina), and on the lot whorl It is apparently always divided 

 Into two thin lines. Between these and the upper peripheral angle, which Is the strongest but not the 

 most prominent on the whorl, the surface Is concave, hut not as deeply so as In G. puldieltttm. The lower 

 keel of the peripheral band Is not always readily distinguished since It Is followed on the slightly v, ntn 

 cose base by six or seven similar though generally somewhat smaller carlnso, while above It then U at 



