304 



Polytremacis a.nd the Ancestry of Helioporidce. 



16. A. E. Ton Eeuss. " Beitrage zur Charakteristik der Kreidescliichten in den 



Ostalpen, besonders im Grosauthale und am Wolfgangsee," *Denk. Akad. 

 Wiss. Wien./ vol. 7, 1854, pp. 1-156, Plates 1-31. 



17. F. W. Sardeson. "Ueber die Beziehungen der fossilen Tabulaten zu den Alcyo- 



narien," ' N. Jabrb. fiir Mineral.' Beilage Band 10, 1896, pp. 249-362. 



18. Tk. Studer. " Versucli eines Systemes der Alcyonaria," ' Arch. Naturgesch.,' 



1887, pp. 1-74, Plate 1. 



19. J. Wentzel. " Zur Kenntniss der Zoantharia Tabulata," ' Denk. Akad. Wiss. 



Wien.,' vol. 62, 1895> pp. 479-516, 5 Plates. 



20. K. A. von Zittel. 'Handbnch der Palaeontologie,' vol. 1, Part 2, 1879. 



EXPLANATION OF PLATE 2. 



Fig. 1. Folytremacis macrostoma, Eeuss. Turonian. Grosau. B.M., 55824. 



Part of tbe external surface of a corallum, showing two calicles partly 

 obliterated by coenenehymal gemmation, and also radial lines of external 

 granules, x 3 diam. 



Fig. 2. Polytremacis parfschi, Eeuss. Turonian. Eussbach, near G-osau. B.M.» 



56,820. Part of transverse horizontal section showing a thick-walled 

 calicle, and the boring of a Leucodorite ; x 10 diam. 



[As the geological history of the Polychaeta is necessarily very imper- 

 fect, it is interesting to note the commensalism of a fossil worm with 

 Folytremacis analogous to that of Leucodora with Keliopora ccerulea; 

 as no anatomical comparison between the recent and fossil worms is • 

 possible, it is advisable to refer to the latter simply as Leucodorites.] 



Fig. 3. JPolytremacis partscM, Eeuss. Turonian. Grosau. B.M., E4149. Trans- 

 verse section across an internal calicle in the Heliopora stage, x 10 diam. 



Fig. 4a-J. Polytremacis partscM, Eeuss. Turonian. Bouches-du-Eh6ne. B.M., 

 E2788. 



„ 4a. Transverse section showing thick calicular wall and radial " costal '* 



arrangement of lamellae, x 10 diam. 

 „ 45. A transverse section across a primitive eaecal group, x 15 diam. 

 Fig. 5a-J. Polytremacis septifera, n.sp. ; copied from Eeuss (16), Plate 24, figs. 



4 and 5. 



„ 5a. Portion of a corallum, natural size. 

 „ 55. Portion of the outer surface, enlarged. 

 Fig. 6a-d. Seliopora ccerulea (Pall.). Eecent. B.M., Zool. Dept. Four parts of 

 a growing edge of a lamellar corallum, surface views, x 10 diam. 

 „ Qa. A group of caeca, all subequal in size. 

 „ 65. A group with enlarged central caecum. 

 „ 6c. A young 'calicle and zone of reduced caeca. 

 „ Gd. An older calicle with septal ridges. 

 Fig. 7a-^. SeliolUes porosus (G-oldf.). Devonian. Seven stages in the develop- 

 ment of a calicle by the fusion of a group of caeca. (After Lindstrom.) 

 X 10 diam. 

 „ 7a. A group of caeca. 

 „ 75. The same slightly developed. 



„ 7<7. The same after the csecal walls have become thinner by partial absorp- 

 tion. 



„ '7d. The same after absorption of the walls of the central caecum forming a 

 calicle made from eight caeca ; the caecal walls remain as septa. 



