KONGL. SV. VET. AKADEMIENS HANDLINGAR. BAND 32. N;0 I. 81 



This pretty coral has chiefly beeii found in uumerous speciiiiens in the liniestonu 

 stratum d. of the VVisby region. There are also specimens from Alnäse and Ryssnäs in 

 Fårö which belong to this species. 



The most characteristic feature lies in tlie formation of the theca and its nailshaped 

 septa, and also in the structure of the exuberant coenenchyina. In a few specimens there 

 are also slight vestiges of shallow pits round the calicles. 



Flasiiiopora scita. Milne Edwakds & Haime. 



Pl. Vir, ftgs. 6 — 18, pl. VIII, figs. 1 — 3. 



1851. Plasraopoia scita M. Edw. & H. Pol. pal., p. 222. 



1864. > » IlD. Brit. Sil. Cor., p. 254, pl. LIX, tigs. 2, 2a. 



1860. » » » H. N. Cor. III, p. 240. 



1867. » » LdM. Nom. Poss. Gotl., p. 27. 



1879. » » QUENST. Petref. Deutsclil. I, p. 145, pl. 148, lig. 32, o, .v, cxcl. u & ij. 



1880. » » NiCHOLSON & EtHERID&E. Girvan, p. 2ö7, tigs. B, C. 

 1880. Plasmopora exscrta IlD. Ibid., p. 269, pl. XVII, tigs. 4, 4a. 



1883. Plasmopora scita Perd. Eoem. Lethasa Geogn., p. 511, tig. 121i;. 

 1885. » » LiNDSTE. List of Foss. Gotl., p. 18. 



1888. » » ID. List of Upp. Sil. Foss. Sweden, p. 21. 



This, perhaps the most common of all our Plasmoporae, assumes as may be before- 

 haiid immagined, a great variety of shapes. It is commonly disciform, having the calici- 

 ferous, superior surface flat or slightly gibbous, but there are also domeshaped colonies 

 or globular and irregularly spheroidal and tuberose. ' 



The calicles are the smallest in the whole genus and scarcely attain one millim. in 

 diameter. As to their form they vary in the highest degree, especially thosc from the 

 stratum d near Wisby, and there might be justified doubts entertained that such extreme 

 forms as those on pl. vii, fig. 6 and fig. 16 could belong to the same species or even to 

 the same genus, were not numerous transitions found between thein, even on the same 

 polypary. 



The common form is represen ted in fig. 6, where the calicles are most regular and 

 the theca entire, its edge a little exsert and tuberculate where the septa continue through 

 it as radii of the aureola. Now it happened that the theca has been, as it were, broken • 

 up in twelve disconnected small pieces (pl. viii, fig. 1) formed by the nodules where the 

 septa cross the theca and continue in the aureola. They become more and more flattened, 

 pl. VIII, f. 2, 3, the boundary line between calicle and aureola vanishes and the broad, flat 

 septa covered with innumerable warts or acuhx; are confluent Avith the coenenchyina, of the 

 tubuli of which only a few indistinctly circumscribed pits remain (fig. 16). That this 

 variety of calicle really belongs to this species is clearly demonstrated by the transverse 

 section (fig. 17) taken a little below the surface, in which the characters of Plasmopora 

 return, to be compared with the other sections (figs. 7, 9, 12, 14, 15), only that in fig. 

 17 the coenenchyma is a little thicker. As represented in figs. 14 and 15 there is also 

 great difference in the proximity of the calicles. 



