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



67 



rely agrees with it in shape and ornamentation. Another common form is similar to 

 Capulus euomphaloides of Mac Coy. There cannot be much doubt that when the various 

 American species of Platyceras, Platystoma and Strophostylus have been sufficiently 

 throughly examined, they may prove to contain many identical forms. Specimens sent 

 to me from Mr S. A. Miller in Cincinnati as Platystoma niagarense, do not in any 

 sensible degree differ from certain varieties of Platyceras cornutum. This, however, in 

 the European strata never attains such a great size as the American ones. 



As to the geological duration of this species it seems to have continued also 

 during the Devonian epoch, as it probably is identical with or nearly related to the 

 Devonian Pileopsis prisca Goldf. p. p. 



2. Platyceras cornutum, var. loricatum n. 



Pl. II, figs. 53—57. 



Shell planorbiform, spire depressed or hidden within the volutions of the large 

 and tumid body whorl. Surface imbricated by transverse, wavy laminas which project 

 in a thin edge, fig. 58, above the surface, and include thickset, threadfine longitudi- 

 nal lines. The transverse lamellse are more distantiated near the aperture than on the spire. 

 The whorls are three or at the highest three and a half, rapidly decreasing in width towards 

 the apex. The aperture is oval or lobate, forming grooves which continue on the body 

 whorl. The sinuosities of the aperture are seen a long way up this whorl through the 

 wavy lines of growth. The inner lip is straight, not reflexed. The spire is often so 

 sunk as to be nearer the umbilical side of the shell than the apical. Height 8 millim., 

 breadth 12 millim., in another specimen height 9 millim., breadth, 15 millim. 



This variety which by transitional specimens is linked to the preceding, has been 

 found near Nya Slitegårds in Dalhem, and in the limestone of Klinteberg. 



3. Platyceras prototypum Phillips. 



Pl. III fiff. 10—18. 



Nerita npvrata^ var. 



Nerita prototypa 



Natica Wenlockensis 

 Äcroculia prototyiia 



Strophostylus cyclostoma 

 Gyclonema brevispira 



1839. Sow. Sil. Syst., 625, pl. 12 f. 15. 



1843. MoKRis Catal. 154. 



1848. Bronn Nomenolat., 806. 



1848. Phillips Mem. Geol. Surv. II, 358. 



1854. MoiiKis Catal. 2d Ed., 264. 



1850. D'OiiB. Prodr., 29. 



1854. Saltek in Siluria 2d Ed., 230 1 



1859. ID. ib. 3d Ed., 548 J P^' ^* *■ °- 



1871. Baily Eigures of Charact. Brit. Possils pt IK 64, pl. XXI f. 11. 



1873. Saltek Catal. Cambridge Foss., 154. 



1864. Hall p. p. Transact. Albany Instit. vol. IV, 218. 



1876. Eeud. Roemee Leth. Geogn. Taf. 14 fig. 14. 



Shell naticiform, globose, with prominent acuminated spire. The ornamentation 

 nearly of the same pattern as in Platyceras cornutum, only finer and denser. There 

 are the same sort of graduated, wavy, longitudinal lines, and elevated, threadfine träns- 



