KONGL. SV. VET. AKADEMIENS IIANDLINGAK. BAND. 19. N:0 6. 81 



never any trace of the .slit band has been found. Of the three varieties which 

 Sandbergek (1. c.) has described, his B. tuinidus comes most near to the Gotlandic 

 form. As to tlie shape it also agrees with the figure given by Sowerby in Silurian 

 System, although it is larger than his. The figure given by D'Ohbigny is altogether 

 different. Bucania trilobata Conrad ') may also belong to this species. Largest dia- 

 meter 18 millim., breadth of aperture 22 mm.; height of aperture 9 raillim., diameter 

 of umbilicus 3 mm. 



It occurs in the .shales of Petesvik in Habblingbo and of Wisby and in the oolite 

 and sandstone of Bursvik. 



Gen. CYRTOLITES Conrad. 



Syiionyras. 1838. Ci/rloliles Conrad Ann. Rep. N. Y. Cal)., 118. 



1838. riiragiimlilhes Conuad p. p. ibid., 119. 



? 1839. Pita.roput! RAFiNRsaUE Bull. Soo. riuol. de France, vol. X, 378. 



184.5. Mioroceras Hai.i, Sillim. .lourn., vol. 48, 294. 



1806. Tropidisciis Meek Proceed. Chicago Acad. Sci., vol. 1, 9. 



1880. Tropidodiscus Waacen (emendatio) Palaeont. Indica XIII, 131. 



1882. Tropidocyclus De Koninck Ann. Soc. Gcol. de Belgique IX, 12. 



Slicll discoid, laterally compressed, involute or tvith free, not co7itiguous lohorls, nin- 

 bilicus oiieii and. double, ajiei'ture elongate and lanceolate. A dorsal keel originates from 

 a sinus or slit in the superior border of the aperture and continues more or less elevated, 

 the intriior lip having its form moidded according to the ivhorl on irhicli it rests. 



In spite of all what has been stated ^) to the contrary, there can be no doubt, 

 nor mistake about the type species of this genus and what its first authors meant 

 thereby. This type is C. ornatus, fir.st named and shortly described by Conrad in the 

 Anruial Report of the Geol. Survey of New York 1838 p. 118 and then again more in 

 full described and figured by Hall in PalEeontology of N. York vol. I p. 308 pi. 84 

 f. 1. There has been almost no dissension amongst the American authors as to this 

 genus. It is of no avail that both Conrad and Hall a few years later united with 

 the first species other fossils, wliich are no Gastropoda at all, being in reality Cephalo- 

 poda, probably Cyrtocerata. ') The fir.st described type must here, as always in similar 

 cases, be the guiding one, around Avhich to group related species and from which dis- 

 similar ones are to be discarded. The other coeval genus, Phragmolithes of Conrad, 

 also coincides with Cyrtolites, as has been shown by Hall in Pal. of N. York vol. I. 

 p. 188, and in which some lines of growth had been interpreted as septa. Dita,rop%is 

 of Raeinesque is a most obscure fossil, but may possibly be only a form of Cyrtolites. 

 Microceras Hall is doubtingly described as septate, but Meek has in Pal. of Ohio vol. 



') TIai.i, Pal. N. York, vol. 2 p. 13, 93. — Planorliis trilobatus Geol. Kep. N. Y., 1838 p. 113. 

 -) Dk Konmnck Faunc Carbonif. II, iv, p. 203. — W'AAnEN Pal;eont. Indioa, Salt Uange Foss. p. I.'i2. 

 •') (!0NiiAi) .loiirnal. Acad. N. Sc. Philadelpiiia vol. 8 p. 270 (C. trcntonensis). Hai.i, Pal. of N. Y. I, 

 p. 188. 



K. Sv. Vi't.-Akad. HnmU. lid. lil. N:o B. ] ] 



