KUNGL. SV. VET. AKAUEMIENS IIANDL. BAND. 19. N:i) 6. 123 



The crescents vary as to their shu])e, as may be seen by the ligures, being commonly 

 dense, regular and distantiuted or tliick and oblique with the greatest bend near the 

 outer lip. But then there are specimens showing, at least for some distance, an angu- 

 larity in the transverse striae instead of the slit band, a conformation quite resembling 

 that which prevails amongst the Euomphalida; and of which also traces are seen in 

 some of the Murchisonia}. 



The whorls are nearly tubular or quite as much rounded on the umbilical as on 

 the apical side although they in some instances seem to be somewhat more flattened on 

 the umbilical side. On the apical side there are on the body whorl about fourteen 

 narrow, longitudinal keels, alternately larger and smaller. The uppermost one, which 

 separates both faces, is the largest of all, blunt and horizontally outstanding. These 

 keels are crossed by regular, elevated, threadlike strite, between which are others still 

 more minute and fine. These meet the slit band on both sides as usual in an acute 

 angle directed backwards. On the umbilical side there are dense, line, transversal 

 striie, bent in a great curve backwards, and then, near the keel, forwards. In some 

 specimens there are as many as seven low, oidy slightly, elevated, longitudinal keels, 

 which are more distinct in the young specimens than in the older ones. In these usually 

 no keels at all are visible. 



The three oldest whorls are tilled with an organic deposit of a solid, calcareous 

 mass, ending in a concave surface, without any sign of diaphragms. In most specimens 

 this apex is often deciduous. The interior whorls are tightly enclosed by the exterior 

 ones, the longitudinal keels of all beino^ interlocked with each other in the interstitial 

 grooves. The whorls have never been found disjointed, though this seems to have 

 been the impression of Hisinger, probably owing its origin to the observation of the 

 nucleus alone, when the uncommonly thick shell had been removed. 



The aperture is circular, approaching to ti-ansversally elliptic, its outer lip being 

 more prominent and protruding, sloping inwards in a gentle sigmoid insinuation. 



Greatest diameter 66 millim. Height of body whorl '12 millim. 



This shell has been found chiefly in the lowest, marly shale beds of Gotland, in 

 numerous specimens, well preserved, at Grogarn and other places of Ostergarn, in the 

 limestone beds of Ardre, and also in the shale of Fardhem, Wisne myr, on which the 

 limestone beds of Sandarfve and Linde repose. From the limestone strata of Oster- 

 garn a single specimen has been obtained. 



Hisinger and Bronn considered this very characteristic shell so much distinct 

 from the so called Euomphali, with which it commonly had been placed, as to create 

 for its reception new genera. It seems that the former in a letter to Bronn in 1835 

 proposed to name it Centrifugus^) led by a mistaken notion that this fossil was iden- 

 tical with the Turbinites centrifugus (jf Wahlenberg ^), which cannot be the case, as that 

 shell rather, as far as can be judged, is either a Pleurotomaria of the evolute form or 

 an evolute Euomphalus, of which both genera there have been s])cciniens found in the 

 Orthoceratite Limestone of Dalecarlia, the only stratum from which Wahlenberg cites 



') Nomenclator p. 256. 



^) Petrificata Tclluris Svecanoe p. 71. 



