HISTORICAL INTRODUCTION. 19 



mens of some Coral or other organism enveloped in a Strouiatoporoid, the "tubes" 

 of Gaunopora being thus adventitious structures. 



In a further communication (' Ann. and Mag. Nat. Hist.,' ser. 5, vol. iv, 

 p. 253, 1879) Mr. Carter returns to the subject of the structure of the skeleton in 

 the Stromatoporoids. He follows Von Rosen in distinguishing two principal 

 types of structure in the skeleton, viz. a " curvilinear structure " and a " rectilinear 

 structure." Mr. Carter also here modifies his previously-expressed view — a view 

 in which at that time most observers concurred — that the " radial pillars " of the 

 Stromatoporoids were solid ; and he comes to the conclusion that they were tra- 

 versed by an axial canal (as in Labechia, E. and H.), but closed superficially. The 

 genus Labechia, E. and H., is placed by Mr. Carter close to Hydr actinia, one 

 ground for this collocation being the supposed encrusting habit of Labechia. It 

 may be certainly stated, however, that Labechia very rarely assumes an encrusting 

 form, the great majority of specimens being in the form of laminar expansions, with 

 a basal epitheca, and a small point of attachment. Lastly, Mr. Carter notices a 

 peculiarity in the appearance of thin sections of certain specimens of Stromato- 

 pora dartingtonensis, Cart, (erroneously identified with 8. elegans, Rosen) — namely, 

 that the stellate canals appear to terminate in the fibre of the coenenchyma itself ; 

 but he gives no satisfactory explanation of this phenomenon. The real reason of 

 this appearance, as will be subsequently more fully shown, is that in this form, as 

 in various others, certain specimens are so preserved that the entire system of 

 canals and internal cavities has been filled with more or less opaque, calcareous or 

 argillaceous sediment, the real skeleton having then been dissolved out, and the 

 spaces thus formed finally filled up with calcite. Hence, in such "reversed" 

 specimens, the canal-system and tubes of the organism have the appearance of 

 being parts of the solid skeleton, while the latter is represented only by trans- 

 parent calcite, and thus looks as if it had been originally hollow, or as if it 

 represented the original ccenenchymal canals and cells. 



In his admirable ' Handbuch der Pateontologie ' (Bd. i, Lief, ii, p. 284, 1879), 

 Professor Zittel treats of the Stromatoporoids under the Hydrocorallines. He 

 includes the genera Labechia,, E. and H., and EUipsactinia, Steinm., in the group of 

 the Stromatoporoidea. 



Lastly, in 1879 the present writer gave a description, accompanied by figures, 

 of the minute structure of the skeleton of the genus Labechia, E. and H. (' Paleo- 

 zoic Tabulate Corals,' p. 330, PI. XV, figs. 4, 4a). In this description it was 

 pointed out that the " pillars " of Jjabechia conferta, Lonsd., are " primitively 

 tubular, but that the median tube is finally largely or entirely obliterated." With 

 regard to the affinities of Labechia, the genus was regarded as doubtfully belonging 

 to the Corals, and was considered as in some respects related to the genus Fistuli- 

 pora, M'Coy. 



