6U G. LINDSTUOM, ON THE SILUKIAN GASTllOPOJJA ANlJ I'TEKOl'OUA OF GOTLAND. 



plate 40 iig. 34, where he luiiues a Carboniferous species as Ilelicites aiirieularis. Next 

 him Fischer von Waldheim comes, who in 1823 in a list on tlie f^enera of Gastropoda 

 ■nves Actita as identical with Capulus and Pileopsis. This is in a treatise called »Ad- 

 versaria zoologicaw Fasciculus III in the Mem. de la Soc. imper. des Nat. de Moscou 

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

 he later in a paper of Fahkenkohl in "Bull, de Moscou» 1844 p. 802 describes an Ac- 

 tita Miinsteriana from the Carboniferous limestone of Moscow. If Fischek really in- 

 tended this genus for the pah\?ozoic forms alone, his name ought to have the priority 

 against the later, 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 later, 1837, in »Letha3a» named Pileopsis cornuta. In respect of the genus he fol- 

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

 boniferous species in the genus Pileopsis. When Conrau in 1840 had founded his ge- 

 nus Platyceras for the pala3ozoic fossils of this group and PiiiLLirs 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 sucli 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 Avere di- 

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

 first who insisted on adopting the genus Capulus of Montfort for the palaeozoic spe- 

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

 in 18G6 ^) announced that they had discovered horseshoe shaped muscular scars on 

 casts of two species, Platyceras subplicatuin and PL infundibulum, almost all authors 

 were unanimous to range these fossils with Capulus. Meek and Worthen, huwever, 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 Plat, subplicatum 

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

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

 the last mentioned authors themselves seem to hesitate with placing it amongst the 

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

 tyceras aiquilaterum from the Burlington beds, without finding in them tiie 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 pakuozoic 

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

 faint and in many specimens not discernil)le, 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 palaeozoic strata. Even if granted that these shells were provided with 



')0r Acrocylia as it ought to be written according to the derivation. 

 • 2) Proceedings Acad. Nat. Sc. Philadelphia 1866 p. 262. 



