46 EXPÉDITION ANTARCTIQUE BELGE 



Microporella divaricata Canu 



PL III. figs. i<i-i 

 Microporella divaricata Canu, Mém. de la Société Geol. de France, 1903. 



Zoarium erect, bilaminate. Zoœcia having the surface only very slightly convex, and 



the sides of the zoœcia straight, separated by distinct Unes, while the distal end is curved ; 

 the entire surface perforated. The oral aperture is fairly large ; about the middle of the front 

 of the zoœcium there is a large semilunate médian pore, and at the proximal end of many 

 zoœcia there is an imperforate semicircular dépression, the same character being marked in 

 the fossil. This I take it, is the commencement of an ovicell, similar dépressions being seen, 

 in Retepora and other gênera, when the ovicells are forming. There are two latéral rosette 

 plates, and two distal ones with numerous pores. 



Onchoporella selenoides Ortmann (') from Japan is very similar, but is not perforated over 

 the surface. 



Monsieur Canu, after seeing mv drawings, showed me this species fossil from Patagonia, 

 named by him Ortmanella divaricata, as he proposed to place it in a new genus. From 

 Patagonia there arc many narrow, bilaminate branching spécimens of this fossil. 



Canu considered that the médian pore did not communicate dircctlv with the interior 

 of the zoœcium in the fossils, and at his request I again examinée! the small Antarctic spécimen, 

 which had when dredged, no doubt been dead some time, so that the soft parts were not 

 préservée!. It is mounted in balsam, which is not the most favorable for the examination ; 

 at any rate I was unable to find any indication of the connection through the médian pore 

 being abnormal. In conséquence of mv remarks, Canu intended to re-examine his fossils, by 

 means of sections, but being for a time, incapacitated from work through illness, he very 

 generouslv placed some of his material at mv disposai for the study of the médian pore. 

 I made mv study on two fossils, frequently examining the longitudinal and transverse sections, 

 during the course of préparation. 



The most important point was the state of fossilisation, for a calcareous deposit has 

 taken place in each zoœcium, sometimes to so great an extent as to nearly fill it up, at other 

 times only forming a thick laver of calcite on the inside of the cell wall. Now when the 

 outer or shell laver is broken away, this internai cast shows the markings of the surface pores, 

 but the médian pore is not found as a larger one. This gives the appearance of there being 

 two layers of shell wall, which is not the case, though it is not very uncommon to find various 

 species of récent Bryozoa, which flake away as if there were two distinct shell layers. 



The filling up of the zoœcial chamber with calcite has made the study more difficult ; 

 however the sections prepared gave no proof of there being a separate chamber into which the 

 médian pore opens. Dark deposits, presumably of iron, are seen in the pore tubes, and often 

 near the inner opening of the médian pore, as well as in other places, but thèse metallic 

 markings, to my interprétation, indicate that there has been organic matter hère, causing 

 précipitation. Thèse dark marks near the médian pore are in the calcite deposit. When Canu 

 is again able to make préparations, he will no doubt check my results, and we shall see if 

 he finds sufficient reason for placing this species in a new genus. 



iii Ortmann, A., Die japanische Bryozoenfauna. (Arch. f. Naturgesch., 1890, p. 28, pi. II, fig. 2.) 



