KONGL. SV. VET. AKADEMIENS HANDL. BAND. 19. N:0 6. 153 



16. Troclius astraliiformis n. 



Pl. XIV fig. 54—58. 



Shell conical, tapering to a narrow ap ex from a broad body whorl. Eight whorls. 

 Their upper boi^der lacerated, as it were, by thick, spinous projections, the base of 

 which completely conceals the adjoining suture. These processes are formed by reflexed 

 folds of the successiva lines of growth, as may best be seen on the umbilical surface 

 of the shell. A little beneath this edge there is a longitudinal bulging out of the 

 whorls. Between the lines of growth the convex surface of the shell is smooth or 

 most finely, transversally striated. The aperture is nearly circular, apiculated in the 

 superior corner, the lips thick and reflexed, the umbilicus is scarcely visible. The 

 sculpture of the umbilical sida consists in thick and coarse callous lines of growth at 

 a regular distance from each other. H. 12 millim., br. 18 mill. A few specimens have 

 been collected at Klinteberg. 



Fam. IX. UMBONIDiE Adams. 



Gen. PYCNOMPHALUS n.^) 



Shell thick, trochiform or glohose, the inner lip of the a-perture ivith a thick callosity, 

 ivhich like a ridge surrounds the umbilicus. 



This genus has been placed amongst the Umbonidas in consequence of the callo- 

 sity, which encloses the wide umbilicus. Most of the other genera have the umbilicus 

 completely covered by a far larger callosity as in Umbonium (= Rotella). 



There is a genus Rotellina De Koninck Faune II, iii p. 92 from the Carboniferous 

 formation of Belgium, Avhich according to the figure given, seems to agree nearly with 

 our, but as the descriptive letterpress expressly states that there is no umbilicus, I 

 have not been sure of the identity and could not refer the Gotland species to it. 



Pitonellus Montfort has also been placed with the Umbonidas, but they have the 

 umbilicus completely covered up. The same is also the case with Umbonium helici- 

 forme Goldeuss from Paffrath. 



As to the identity of this genus with Platyschisma see below in Pychn. acutus. 



Of the genus Pycnomphalus I have found the following three species in Got- 

 land. 



1. Pycnomplialus otoesus n. 



Pl. XV fig. 64—67. 



Shell helicoid, with five ventricose whorls in a short spire. There are no orna- 

 ments excepting some indistinct, transverse lines, which are curved backwards. The 

 aperture is circular, the outer lip thin, the inner lip thickened through an accumula- 

 tion of the shelly matter, nearly five times as thick as in the outer lip. The umbilicus 



') Ilvxvng, dense, thick, oftcpalng, umbilicus. 



K. Vet. Akad. Handl. Band 19. N:o O 20 



