852 THE PALEONTOLOGY OF MINNESOTA. 



[Bellerophontlldse . 



subcordiform, widest in the middle or below, without callosities of any kind, nor 

 with a sinus in the outer lip. From the aperture to a point about half around the 

 dorsal circumference of the last volution there is a narrow open slit lying between 

 two sharply elevated edges; behind this point the slit is closed over and forms an 

 ordinary slit-band with distinct lunulae. Surface with close or distant transverse 

 imbricating lamellae, the anterior edges of which are zigzagged and sometimes 

 greatly spread out. Lamellae plicated, the successive folds often arranged so as to 

 form small revolving ridges; over all very fine lines of growth. Type, C. obliqua 

 U. & S. 



C. flmbriata U. & S. Stones River group. (7. imbricate Meek & Worthen sp. Trenton gr. 



C. triangularis U. & S. Stones River group. C. eltgans Miller. Loraine group. 



C. grandis Ulrich. Stones River group. C. bellula Ulrich. Loraine group. 



C. obliqua U. & S. Black River group. C. dyeri Meek. Richmond group. 



C. oompressa Conrad sp. Trenton group. C. dyeri, var. cellulosa U. & S. Trenton. 



C. similis Ulrich. Trenton group. C. pannosa Billings. Hudson River group. 



OXYDISCUS, Koken.* (Tropidodiscus, Meek,f Waagen^:, not Steininger, 1855.) 

 Strongly compressed, disciform shells; volutions embracing very little, expanding 

 gradually to the aperture, sharply keeled; aperture somewhat lanceolate or subtri- 

 angular, without an inner callosity; outer lip with a deep V-shaped excision, 

 continuing in the dorsal keel as a long and very narrow slit; behind the slit the 

 summit of the keel may show a more or less distinct band with lunulse, or merely a 

 delicately bordered raised line. Surface markings consisting of growth lines only. 

 These bend strongly backward in passing from the ventral side of the whorl to the 

 keel. Type, 0. imitator Koken. 



A M 1:1: ii AN SPECIES. 



O. acutus Sowerby sp. Lower Silurian. O. cristatus Saflord sp. Trenton. 



O.disculus Billings sp. Black Riv. and Trenton. O. magnus Miller sp. Cincinnati. 



O. subacutus Ulrich. Trenton. O. curvilineatus Conr. sp. Schoharie grit and Up. Held. 



According to Koken Euomphalus strongi Whitfield, a " Lower Magnesian " fossil, 

 probably belongs here. 



EUROPEAN SPECIES. 



O. (Euomphalus) planissimus Elchwald. Low. Silur. O. (Cyrtoliles) orbiculus Lindstrom. Up. Silurian. 

 U. (1'orcellia) scutigerus Eichw. Upper Silurian. U. (Cyrtolitts) delanonii (Ehlert. Low. Devonian. 



O. (Cyrtolites) discus Lindstrom. Upper Silurian. O. imitator Koken. Middle Devonian. 



Family BELLEROPHONTIID.E. 



Symmetrically involute shells, the whorls enlarging rapidly, the mouth gener- 

 ally expanded laterally and ventrally, not dorsally, the umbilicus mostly small or 

 closed. Inner lip more or less thickened, the outer sinuate and centrally emarginate, 



N. Jarlibuch f. Mlneralogle. etc., Belluneband vl, p. 390; 1889. 

 t Proc. Chicago Acad. Sci., vol. I. p. >J; I860. 

 t Pal. Indira, s.-r. 13. pt. 2, p. 131; 1880. 



