334 TABULATE CORALS. 



central depression at their apices, which would appear to show 

 that the central tubes of the columns are really sometimes open 

 above. In specimens which have been slightly weathered, 

 also, one may often recognise under the microscope the exist- 

 ence of an unmistakable central tube in the columns, though I 

 certainly cannot affirm that I have ever been able to detect 

 any openings to which the name of " calices " could be applied. 



The interspaces between the columns in the skeleton of 

 Labechia are entirely filled (fig. 44, c) with a cellular tissue 

 formed by curved calcareous lamellae, which have their convex- 

 ities directed upwards, and give rise to a series of lenticular 

 vesicles which extend from the epitheca below to the surface 

 above, and appear to be bounded superiorly and superficially 

 by a delicate calcareous membrane. In tangential sections (PI. 

 XV., fig. 4) the cut edges of the curved lamellee which form 

 the lenticular vesicles appear as irregular curved lines extend- 

 ing between the transversely-divided columns, and subdividing 

 the intervening space into irregular compartments. Both in 

 vertical and in tangential sections, the appearances presented 

 by the interstitial tissue present some curious resemblances to 

 those exhibited by species of Fistulipora (such as F. vtinor, 

 M'Coy, and F. mcrassata, Nich.), in which the tabulae of the 

 small corallites coalesce and give rise to vesicular tissue. 



Having now briefly discussed the intimate structure of La- 

 bechia, it remains to make a few remarks upon its possible afifin- 

 ities and systematic position. The most recent and most widely 

 adopted theory upon this subject is that put forward by Dr 

 Lindstrom (Ann. Nat. Hist., ser. 4, vol. xviii. p. 4). Accord- 

 ing to this acute observer, the skeleton oi Labechia in its earliest 

 stages of growth consists of " a very thin circular disc, with 

 concentric lines of growth beneath, and having the superior 

 surface studded with blunt spines, which radiate from the cen- 

 tre, and also coalesce and form continuous ridges. In this state 

 it reminds one of nothing more than the sclerobasis of the 

 Hydrozoan genus Hydractinia ; and the only difference seems 

 to be that Labechia is entirely calcareous, whilst Hydractinia 



