So EXPEDITION ANTARCTIQUE BELGE 



from the figures and descriptions, as unreliable characters were used. From the Miocène 

 of N. America it occurs as Phidolophora Gabb. and Horn. In the Pliocène of England, Italy 

 &c. there are various species of Retepora ; and a number hâve been described from the upper 

 Tertiaries of Australia by MacGillivray and others. In ail probability the genus has never 

 before reached so high a stage of developement, it is universally distributed, and is evidentlv 

 abundant in both polar régions. The distribution of the species of Retepora is as a rule very 

 limitée!, more so than that of any other large genus. 

 The number of tentacles are : 



R. protecta nov. 12. R. hippocrepis nov. 11. R. Couchii H. 12. 



R. frigida nov. 14. R. laevigata nov. i5. R. cellulosa L. 12. 



R. antarctica nov. 14-15. R. lepralioides nov. 13-14. R. elongata Sm. i5-i6. 



Retepora antarctica sp. nov. 



(PI. VI, figs. ia-k) 



Zoarium reticulate, forming flat expansions with fairly large meshes. The fenestrae are 

 about the same width as the branches, which as a rule are about o.6 mm wide. 



One pièce from N° 620 is nearly flat and measures about /[5 mm X 3o mm . 



Zoœcia rhomboidal, separated on the anterior surface by distinct slightly raised lines, 

 with the peristome considerably elevated at each side, and usually a sinus to the secondary 

 triangular aperture. Anterior and posterior surface somewhat granular ; with small elliptical 

 avicularia on the front of the zoœcia, sometimes depressed, occurring in some pièces generally 

 to each zoœcium, or even there may be a second avicularium, while in other pièces the avicularia 

 are only found on a small proportion of the zoœcia. In some spécimens there are a few 

 avicularia, with broadly triangular mandibles, at one side of the proximal border of the peris- 

 tome ; and very rarely there is a large raised transverse triangular avicularium, with long 

 triangular mandibles (fig. ic). There are on some young zoœcia 4 oral spines, and in the 

 interior of the zoœcium there are two calcareous projections for the attachment of the operculum 

 (see fig. 1/;). The operculum becomes much wider at the proximal edge. The ovicell has no 

 slit or other markings, except where the zoœcial dividing lines extend over it ; they often 

 contain embryos. On the dorsal surface the vibices are irregular and there are a few elliptical 

 avicularia. The oral glands are well developed, and the number of tentacles is 14-15. 



There is a large dark mass in some of the tentacles, but I hâve never found more than 

 one such tentacle in a zoœcium, and it may occur in the tip, when histolysis has commenced 

 at the extremity, and near it the remaining cells are few and not distinct, while lower down 

 they are but slightly changed. In some cases however there is in thèse stained sections a dark 

 mass about the middle of the tentacle, and close to it ail the cells hâve disappeared, while by 

 the extremity they are in their usual places. Dark bodies in the tips of Smittia gelida nov. &c. 

 hâve been already referred to, but the two cases are not quite similar, as in S. gelida the tips, 

 of practically ail the tentacles, contain thèse bodies, whereas in the présent case there are only 

 a very limitée! number of such tentacles, and never more than one such to any zoœcium. 

 Spécimens in différent conditions of growth must be studied, before we can be sure what 

 spécifie différences there are. 



