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



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

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

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

 System, although it is larger than his. The figure given by D'Orbigny 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 millim., diameter 

 of umbilicus 3 mm. 



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

 and sandstone of Biirsvik. 



Gen. CYRT0LITE8 Conrad. 



Synonyms. 1838. Cyrtolites Conrad Ann. Eep. N. Y. Oiib., 118. 



1838. PJiragmolithes Conrad p. p. ibid., 119. 



? 1839. DitcLvopus Rapinesöue Bull. Soc. Géol. de France, vol. X, 378. 



1845. Microceras Hall Sillim. Journ., vol. 48, 294. 



1866. Tropidismis Mbek Proceed. Chicago Aoad. Sci., vol. 1, 9. 



1880. Tropidodisciis Waagen (emendatio) Paloeont. Indica XIII, 131. 



1882. Tropidocyclus De Koninck A.nn. Soc. Géol. de Belgique IX, 12. 



Shell discoicl, laterally coin]jressed, involute or loitli free, not contiguous ivlwrls, um- 

 bilicus open and double, aperture elongate and lanceolate. A dorsal keel origina.tes from 

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

 the interiör lip having its form moidded aceording to the ivhorl on lohich it rests. 



In spite of all what has been stated ^) to the oontrary, 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, first named and shortly described by Conrad in the 

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

 full described and figured by Hall in Palajontology of N. York vol. I p. 308 pl. 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 låter united with 

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

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

 cases, be the guiding one, around which 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 Fal. of N. York vol. I. 

 p. 188, and in which some lines of growth had been interpreted as septa. Ditaxopus 

 of Rafinesque 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 Fal. of Ohio vol. 



') Hall Pal. N. York, vol. 2 p. 13, 93. — Planorbis trilobatus Geol. Rep. N. Y., 1838 p. 113. 

 ^) De Koninck Fanne Carbonif. II, iv, p. 293. — Waagen Palajont. hulica, Salt Ilange Foss. p. 132. 

 ■') CoNiiAD Journal. Acad. N. Se. Philadelpliia vol. 8 p. 270 (C. trent.onensis). Hall Pal. of N. Y. I, 

 p. 188. 



K. Sv. Vet.-Akad. HandL Bd. 1!). N-.o 6. 11 



