THE ANTHOZOA PÉRFORATA OF GOTLAND. 7 



those flinty balls, by the islanders called »eitlar» J ) one may in almost every instance feel 

 assured that it is a detached or worn fragment of the same fossil. This fossil is thus 

 found almost everywhere, as well in the oldest shale beds as in the youngest, limestone 

 cliffs and in the most distant parts of the island. Being of so wide a range both in a verti- 

 cal and a horizontal sense it is not surprising that the fossil has assumed a great variety 

 of shapes. The various ways in which it has been preserved or metamorphosed by che- 

 mical agencies also give a deceptive appearance to its exteriör and interiör structure. The 

 organic tissue is, especially in the large ball-stones of Östergarn, sometimes, as it were, 

 almost effaced, and it is only by inference, from other balls and by faint indications of 

 the calices one is able to conclude that they once had the same origin as the unaltered 

 balls. In the same ball changes also can be traced from the regular coralline structure 

 to an inorganic mäss of limestone, where no indication is left of the totally changed 

 coenenchyma. At first. sight it is highly doubtful whether to consider those specimens 

 found at Wisby identical with them from Östergarn or more particularly from Kräklingbo, 

 bnt having compared a large number and examined sections of the interiör structure I 

 can see no specific differences, but only such unessential as arise from local fluctuations in 

 the mode of growth, inflnenced by occasional exteriör agencies. I shall then first describe 

 what I think to be the more typical and regular variety of this coral, as found at Wisby, 

 then to notice the other varieties. The coral is compound, and forms large, flat masses 

 shaped like lenticular disks. The basal surface is nearly Mat or a little uneven, concen- 

 trically wrinkled by the successive lines of growth, as common among the compound 

 corals. It is also coated with a very thin layer of epitheca. The upper surface is more 

 or less hemispherical and tending to increase most rapidly in the middle, thereby gaining 

 in height in that part so as to be more or less conical. At somewhat regular distances 

 of about 3 millim. it is provided with irregular stellular openings or calices of six, but 

 also seven or eight much branching and subdivided rays, which meet very closely in their 

 centre, and leave only a very insignificant opening betAveen them. The width of the 

 calices varies between 5 and 10 millimeters. The calicular rays become at their ends con- 

 fluent with the abundant coenenchyma of which the chief mäss of the coral is made up. 

 It consists of a spongious tissue formed by interlaced sclerites branching and coalescing 

 amongst themselves. In its growth it has had regular periods of rest, so as to form se- 

 parate layers of sclerenchyina of the utmost thinness, which layers generally are without 

 connection with each other. Sometimes nevertheless several thin layers are intermingled 

 and soldered together in thicker strata. Owing to the formation of such concentric strata 

 the ballstones break up in a mäss of concentric laminse when exposed to the agency of 

 the air. The thin layers are often scarcely amounting to half a millimeter. — The coral 

 had almost always affixed itself to other ruarine animals, evidently living and for a time 

 struggling with their fast spreading and overwhelming invader. So it often happens that 

 the surface of Coenostroma is elevated into regularly distributed conical prominences, 

 caused, as easily seen through a section, by Cyathophylla that had been surrounded b 

 the Coenostroma and overgrown by it, having striven for a while in vain till they were 



l ) »Eitel» pl. ar, a gland or kernell, from the icelandic »eitill» a härd knob. 



