Mr. H. J. Carter on Stromatopora dartingtoniensis. 341 



the coral : but it is not so really ; for on closer examination 

 they will not only be found to be more or less in equidistant, 

 but often more or less oblique, showing that the growing 

 surface of the coral must have always been so far irregular or 

 pitted ; hence the tabulae in the tube of Favosites &c, although 

 generally, are not always equidistant, and are often more or less 

 oblique. This irregularity is well illustrated in Mr. Ber- 

 jeau's faithful drawnings at the end of Nicholson's valu- 

 able work on the Tabulate Corals of the Palaeozoic Period 

 (Blackwood and Sons, Edinb. 1879) ; while sometimes they 

 are scarcely, if at all, distinguishable from the rest of the 

 homogeneous transparent calcspar which fills the tube. It is 

 necessary to remember all this ; for it will tend to explain what 

 may hereafter be stated of the tabulation in the " stellate 

 venation," or astrorhiza, of Stromatopora, viz. the irregular 

 disposition of the tabulae as regards distance, direction, and 

 definition, they being sometimes, although present, undistin- 

 guishable from the rest of the calcspar filling the tubes. 



Astrorhiza. — In my paper " on the Structure of Stroma- 

 topora'''' ('Annals,' 1879, vol. iv. p. 258) I have described 

 the stelliform parts of the coenosarcal cavities under the head 

 of " stellate "venation ;" but this term is not sufficiently ex- 

 pressive for the defined and characteristic feature which this 

 part of the coenosarcal structure generally presents ; hence I 

 shall hereafter substitute for it " astrorhiza," as fulfilling 

 the purpose better, at the same time that it is more in accor- 

 dance with the term " hydrorhiza," already applied to the 

 root-like or originating portion of Hydroid Zoophytes ; for the 

 astrorhiza, according to my view, is homologous with the 

 " stolon-like tabulation," which is put forth from the embryo 

 of Hydractinia echinata for the development of the individual, 

 whose horny structure or coenenchyma is formed upon a filament 

 of the same kind of coenosarc as that which pari passu covers 

 its exterior and produces the polypites (' Annals,' 1877, 

 vol. xix. p. 46, pi. viii. fig. 3c, &c), whereby the astrorhiza 

 becomes in plurality (PI. XVIII. fig. 2, a a a) the origin of 

 each lamina of the Stromatopora, through which the whole 

 mass is finally produced. 



Those who have read Mr. H. N. Moseley's admirable 

 paper " On the Structure of Millepora " &c. (Phil. Trans. 

 1877, vol. clxvii. pt. l,p. 117) must have observed (at p. 125) 

 that he uses the term " hydrophyton " for the whole of the 

 coenosarc in Millepora as " homologous with the hydrorhiza 

 of other hydroids ;" but inasmuch as Mr. Moseley finds it 

 necessary afterwards to make a distinction between the 

 " main canals " and the smaller ramifying ones which con- 



