HUYOZOA OF THE PHILIPPINE REGION 253 



"In Petralia rultur Ilincks var. armata Waters, on the dorsal sur- 

 face there are perforated spaces, no doubt for radicles, but there are 

 usually several small ones instead of one large one as in Lepralia 

 dorsiporosa Busk." (Waters, 1913.) 



"It may be considered as a good family character that the basal wall 

 in all these species is provided with pores, which otherwise appear only 

 very exceptionally on the basal wall of free, one-layered colonies within 

 the division Ascophora. Whilst these pores occur scattered over the 

 whole of the basal wall in P. undata and P. japonica, in all the other 

 species they appear in one or more, rarely several (P. dorsiporosa) 

 pores chambers, which are situated at the distal end of the basal 

 wall." (Levinsen, 1909.) 



On the interior face, each zooecium bears in the distal regions a 

 more or less large fosctte, elliptical or circular, at the bottom of 

 which is a calcareous membrane finely perforated; this is the "per- 

 forated area" of Waters, who claims that it is intended for the 

 insertion of a large radicle. We have not been able to verify this but 

 we know that Waters is too good an observer to publish a statement 

 without verifying it. A chitinous membrane often closes this facette, 

 especially on the zoarial margins. 



Around the perforated area there are frequently some small pores 

 which are radicular; the radicles are very fine and cling especially to 

 algae or to small shells. 



The radicular pores as well as the perforated area have a very 

 variable size, even on the same zoarium. We have had the occasion 

 to study these variations on the species described. 



Septules. — "The distal half of each lateral wall is provided with 

 3 to 8, as a rule few-pored, very rarely uniporous, rosette-plates." 

 (Levinsen, 1909.) 



"In Petralia chuakensis there are numerous uni or few-pored rosette- 

 plates (septules) scattered over the distal wall.. On the lateral wall, 

 about halfway between the frontal and basal walls, there is a row of 

 about 5 few-pored rosette-plates." (Waters, 1913.) 



Ovaria. — In Petralia chuakensis, in the ovarium there are but few 

 ovarian cells." (Waters, 1913.) 



Genus PETRALIA (MacGillivray, 1887), Levinsen, 1909 



The ovicell is hyperstomial, always closed by the operculum, deeply 

 immersed in the distal zooecium. The poster is wider than the anter. 

 The shield is a regular smooth pad around the aperture; it bears 

 sometimes two small lateral avicularia, 25 or 26 tentacles. The 

 radicular pores are numerous. 



Genotype. — Petralia japonica Busk, 1884. 



/i<i!ige. — Recent. 



