KONGL. SV. VET. AKADEMIENS IIANDLINGAU. BAND. 19. N:0 6. 85 



It is distiiiguished from the following through its fevvur and broader whorls, 

 through its lower and bluut slit band and its triangulär aperture. 



7. Cyrtolites orbiculus n. 



ri. VII ligs. 16—17. 



Shell discoid, involute with all whorls contiguous. Surface with distantiated, 

 threadfine, elevated, transverse lines, gently curvud backwards, the interstices being 

 suiootli or indistinctly finely striated. The whorls are five and a half, at highest near 

 their inner edge, which sinks vertically to the deep suture. Aperture broadly lanceo- 

 late. Slit band a thin, piwninent keel ujore elevated than in any other Gotland spe- 

 cies of this genus. 



Lai'gest diameter 13 millim; thickness 4 niillim. at the aperture. Only one spe- 

 cimen has hitherto been found in the shale of Djupvik in Eksta. 



Gen. TREWIANOTUS Hall. 



1864 Tremanotus Hall Extraet of ISth liept. St. Cab. N. York p. 43. 



1868 Gyrotrema Barkande, accordiiig to Bjgsby Thes. Silur. p. 167 and also to letters from M. Bariiande 



himself. 



Shell discoid, involute, whorls tumid, visible both from the umbilical and cvpical side, 

 consequently with large, open, double umbilicus; aperture with greatly expanded and enlarged 

 lips, the slit very shallow, continuing in a narrow keel, which is perforated by a nuniber 

 of oval apertures. These have subsequently been closed with shelly matter. 



This genus was founded by James Hall, as is stated by Meek^), in an Extraet 

 from the 18th Report of Regents N. York. St. Cab. p. 43, which was issued in 1864, 

 but this extraet was never published along with the rest of the 18th Report"), being 

 only in 1868 joined to the first edition of the 20th Report, with the date 1865 printed 

 on the slieet wherein the said description is contained. It seems, however, not to be 

 any valid grounds to follow Hall in placing it as a subgenus to Porcellia, a genus 

 Avhich belongs to a much låter period and has a deep slit in the exteriör lip and a 

 slit band quite as in Pleurotomaria, but without apertures and, moreover, obliquely spi- 

 ral. Tremanotus is indeed quite as much different from this genus as from all other 

 Bellerophontidai, excepting Tubina and possibly also Salpingostoma, in the presenee of 

 the apertures on the doi-sal keel. It resembles, as to the expanded aperture, some of 

 the species of Bucania, which genus, as it has been limited by its founder FIall in 

 the Pal. of N. York vol. I, contains many heterogenous forms, of which several ones 

 are extant only in obscure casts. Amongst other genera, Tubina Barkande^) is related 



1) Meek Proc. Chicago Ac. Se. 1865, vol. I. p. 10. 



-) Issued in 1865. 



*) OwEN Palaeontology 1860 p. 71 lig. 71, 8 and also uamed tlius on labcls in collections sent from Prag. 



