KONGL. SV. VKT. AKAUEMIENS HANPLINGAK. liANI). 19. N:() 6. 85 



It is (listiiiguislicd Iroiu tlie (olhjwiiig tliruLigli its t'mvcr and broader whorls, 

 throui;h its lower and blunt slit band and its triangular aperture. 



7. Cyrtolites orbiculus n. 



PI. VII tigs. 16—17. 



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

 threadline, elevated, transverse lines, gently curved backwards, the interstices being 

 smooth or indistinctly linely .striated. The whorls are live and a liall', at highest near 

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

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

 cies of this genus. 



Largest diameter 13 millim; thickness 4 millim. at the aperture. Only one spe- 

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



Gen. TREMANOTUS Hall. 



1864 'J'riiuaiiola^ Hall Extract oi' 18th Kept. St. (,'ab. N. York |). 43. 



1868 Gyrolrema Barrandk, according to Bjgsby Tbes. Silur. p. 167 and also to letters from M. Bahkanue 



himself. 



Shell diacoid, involute, whorls tumid, visible both from the umbiiieal and apical side, 

 conse(jue7itii/ with lan/e, open, double umbilicus; aperture with greatly expanded and erdarged 

 lips, the slit very shallow, continuiny in a narrow keel, which is perforated by a number 

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



This genus was founded by James Hall, as is stated by Meeiv*), in an Extract 

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

 but this extract was never publislied 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 sheet 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 

 which belongs to a much later period and has a deep slit in the exterior lip and a 

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

 ral. Tremanotus is indeed quite as much difl'erent from this genus as from all other 

 Bellerophontidic, excepting Tubina and po.ssibly also Salpingostoma, in the presence of 

 the apertures on the dorsal keel. It resembles, as to the expanded aperture, some of 

 the species of Bucania, which genus, as it has been limited by its founder Hall 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 Bakkande^) is related 



') Meek Proc. Chicago Ac. Sc. 1865, vol. I. p. 10. 



-) Issued in 1865. 



^) Owen Pala;outology 1860 p. 71 lig. 71, 8 and also named thus on labels in cullections sent from I'rag. 



