GO G. LINDSTRÖM, ON TUE 8ILUKIAN GASTUOPODA AND PTEKOrODA OF GOTLAND. 



plate 40 fig. 34, where he nauies a Carbonifcrous species as Helicites aiiricularis. Next 

 hiin FiscHER von Waldheim coines, who in 1823 in a list on the genera of Gastropoda 

 gives Actita as itlentical witli Capulus and Pileopsis. This is in a treatise called »Ad- 

 versaria zoologica» Fasciculus III in the Mém. de la Soc. impér. des Nat. de Moseou 

 vol. VI p. 234. That he therein also included the palteozoic species is evident, when 

 he låter in a paper of Fahrenkohl in »Bull. de Moseou» 1844 p. 802 describes an Ac- 

 tita Ministeriana from the Carbonifcrous limestone of Moscow. If Fisciier really in- 

 tended this genus for the pahi30zoic forms alone, his name ought to have the priority 

 against the låter, as Platyceras, but it is by his first publication evident that he gave his 

 genus quite as wide limits as already had been given to Capulus and Pileopsis. Actita 

 then must be considered only as a synonym. In 1828 Hisinger in his Anteckningar, 

 pt. 4, p. 221 mentions a Turbinites, which he also figures, and this is the same which 

 he låter, 1837, in »Letha^a» named Pileopsis cornuta. In respect of the genus he fol- 

 lows the elder Sowerby, who 1835 in his Mineral Conchology placed the English Car- 

 bonifcrous species in the genus Pileopsis. When Conrad in 1840 had founded his ge- 

 nus Platyceras for the palasozoic fossils of this group and Phillips in 1841 his genus 

 Acroculia^) for the same, the subsequent American authors sided with their countryman, 

 and the English ones with their, in spite of the former name having the priority and 

 that with such a tenacity that it lasted until 1851 when S. P. Woodward in his Manual 

 accepted Platyceras instead of Acroculia. Besides, the opinions of the authors were di- 

 vided between accepting the older genera Capulus or Pileopsis. De Koninck is the 

 first who insisted on adopting the genus Capulus of Montfoet for the pala^ozoic spe- 

 cies and especially those of the Carbonifcrous formation. Since Meek and Worthen 

 in 1866^) announced that they had discovered horseshoe shaped muscular scars on 

 casts of two species, Platyceras subplicatum and Pl. infundibulum, almost all authors 

 were unanimous to range these fossils with Capulus. Meek and Worthen, however, ex- 

 pressed as their opinion that these fossils »probably» are »distinct from the existing 

 genus Capulus», but that they are more nearly allied to that group than is generally 

 supposed to be the case. Moreover it may be questioned whether Plåt. subplicatum 

 and kindred really belong to the same genus at the Silurian ones. It bas been found 

 only in casts. As to the other species, of which only one specimen has been found, 

 the last mentioned authoi's themselves seem to hesitate with placing it amongst the 

 Platycerata. I have myself studied the interiör surface of several specimens of Pla- 

 tyceras ajquilaterum from the Burlington beds, without finding in them the least trace 

 of any muscular scars. Nor have I been able to find any muscular impressions in the 

 numerous specimens of the Silurian forms which I have examined. But this can, 

 however, not be conclusive as to the deficiency of the muscular scars in the pala^ozoic 

 species, because even in recent or tertiary Capuli the muscular impressions are very 

 faint and in many specimens not discernible, owing to the glossy surface of the shell. 

 It must then be very difficult and a thing of rare occurrence to detect them in spe- 

 cimens from palasozoic strata. Even if granted that these shells were provided with 



') Or Acvocylia as it oiiglit to be written according to the derivation. 

 -) Proceedings Acad. Nat. Se. Philadelpliia 1866 p. 262. 



