Tabulate Corals with Existing Species. 357 



others allied to Porites and Madrepora^ have true tabulae ; also 

 the genus Astrceojysammiay V., of the Eupsammidce ; the species 

 of Pocilloporaj a genus closely allied, in its animals and other- 

 wise, to Ocidina and Stylophora^ have very numerous and per- 

 fect transverse septa | even among the Alcyonaria, the genus 

 Tubipora occasionally has transverse internal septa ; and the 

 same is true of Millepora^ belonging to the class of Acalephs. 



Notwithstanding the very slight basis upon which the group 

 of " Tabulata" was established, and disregarding the very 

 great and important differences which exist among the corals 

 thus unnaturally brought together, most writers upon corals, 

 whether recent or fossil, during the past twenty years have 

 adopted this classification without hesitation. 



And yet this is but another instance forcibly illustrating the 

 general rule that classifications based on single characters are 

 very likely to be artificial and erroneous. It also illustrates 

 the manner in which such an error often leads to others of still 

 greater importance. 



In 1857 Professor Agassiz made the very important disco- 

 very that the animals of Millejjora are not true polyps^ but 

 genuine hydroids^ belonging to the class of Acalephs or 

 MeduscB^ . But, since MiUepora is a genus belonging to the 

 " Tabulata," he immediately concluded that all the " Tabu- 

 lata" are, therefore, hydroid Acalephs! And, not content 

 with this sufficiently bold generalization, he extended it 

 likewise to the extinct " Rugosa " or Cyathophylloid corals f, 

 at first apparently with some hesitation, but more recently 

 without qualification \. 



From this conclusion, if admitted, it followed that in the 

 Palaeozoic ages there were few, if any, true polyp-corals, but, 

 on the other hand, the class of Acalephs was abundantly re- 

 presented by a great variety of coral-making forms, some of 

 them of great size, and capable of building extensive coral- 

 reefs, similar to those made by true polyp-corals in modern 

 times ! Thus the geological importance of these two classes 

 of animals would be completely reversed, as well as our ideas 

 of the nature of corals and coral-reefs. 



These views have been held and advanced by Professor 

 Agassiz for many years, and have been urged quite recently, 



* Proceedings of the Boston Society of Natural History, vol. vi. p. 373, 

 1859. See also Pourtales, in Illustrated Catal. of the Mus. of Comp. 

 Zoology, no. 4, p. 56, 1871. 



t Contributions to the Natural History of the United States, vol. iii. 

 pp. 61-63, and vol. iv. pp. 292-206 & 338. 



t Bulletin of the Museum of Comparative Zoologv, vol. i. no, 13, p. 384, 

 1870. 



