Introduction. 



The purport of tliis ineinoir is chiefly to review the Swedish species belonging to 

 the paJa-ozoic corals of the family of the Heliolitidiv, also paying due attention to several 

 species from other regions, which give good illustrations of the structure and the deve- 

 lopment. To the genuine Heliolitida? I append the Coceoserid.p, which in some instances 

 have been described as Heliolita' and which I consider to be a group nearly related to 

 them. 



The material for attaining this scope has been derived chiefly from the island of 

 Gotland, being very rich in such fossils, but also from other phices in the mainland of 

 Sweden, as well as from all other countries where Silurian and Devonian formations exist, 

 excepting Australia. 



My thanks are due to many naturalists, some now deceased, for valuable contributions 

 to ray work, through sending me with great liberality specimens and much useful infor- 

 mation. I am thus under great obligations to Signor G. de Angelis D'Ossat in Rome, 

 to the late Mr Billings, Professors Douvillé, Frech, Mr J. E. Gray, late of Hagley, 

 Dr J. W. Gregory, the late Dr J. Hall of Albany, Drs Head (Chicago), Hinde, Holm, 

 Professors Ths. M'Kenny Hughes, Inostranzew, von Koch, von Koenen, Laube, Malaise, 

 Alph. Milne-Edwards, Nicholson, M. D. Oehlert, Dr Penecke, Prof. Pocta in Prag, 

 Prof. Ferd. Roemer, Dr Rominger, Prof. Schluter, Akadem. Fr. Schmidt, Prof. Hj. 

 Théel, Drs TöRNQUisT, Wentzel, Wiman, and H. Woodward. 



It has been the more welcome to receive such friendly assistance as the Identifica- 

 tion of many species is very difficult through unsatisfactory descriptions and bad or in- 

 complete figures. Through the scients above mentioned I have received for inspection 

 several critical specimens which have formed the basis for descriptions by previous authors. 

 It is, of course, most important to examine such specimens and compare them with others 

 because there may, especially in respect to the oldest descriptions, be some uncertainty 

 of what forms were kept in view. 



With very few exceptions, especially mentioned, a great number of specimens have 

 in each species been examined, in some instances more than hundred, and studied in 

 transparent sections. 



K. Sv. Vet. Akad. Handl. Band 32. N.-o 1. 1 



