250 BULLETIN 100, UNITED STATES NATIONAL MUSEUM 



versely striated. The aperture is semielliptical, transverse. The 

 ovicell is hyperstomial, closed by the operculum, small, convex, 

 pointed distally. Each zooecium is surmounted by a small orbicular 

 avicularium without pivot. 

 Measurements. — 



Aperture!** ^J™' ZooeciJf 2 =°- 3 c 5 mm ' 



[la =0.075 mm. \lz =0.25 mm. 



Affinities. — This new species differs from Chorizopora brongniarti 

 Savigny-Audouin, 1826, in its much wider zooecia with a quite different 

 aspect. Our specimen was dead and was encrusting a Stylopoma 

 itself growing on a Tridacna. 



Occurrence. — From an unknown Philippine locality associated with 

 Stylopoma grandis. 



Holotype — Oat. No. 7998, U.S.N.M. 



Family PETRALIIDAE Levinsen, 1909 



The ovicell is hyperstomial; it is formed of an olocyst surmounted 

 by a tremocyst with very small pores. The aperture is surrounded by 

 a shield placed next to the tremocyst. On the inferior face of the 

 unilamellar colonies there is at the distal extremity of each zooecium 

 a perforated area with small radicular pores. 



Levinsen, 1909, thought that many genera could be recognized in 

 this family. In fact we have been able to distinguish three genera 

 in the material from the Philippines, following the usual rules of our 

 classification. These are Petralia (MacGillivray, 1887) Levinsen, 

 1909, Petraliella and Coleopora Canu and Bassler, 1927. Although 

 the genus Petralia is perfectly characterized by its genotype, we con- 

 tinue to classify here all the species which we have been unable to 

 study or to place in the two following genera. Petralia tuberosa 

 Busk, 1884 is very probably the type of a new genus. 



Compensatrix. — "The compensation -sac of Lepralia dorsiporosa 

 Busk, 1884, is seen with great distinctness in a decalcified preparation. 

 It underlies the whole of the frontal wall on the proximal side of the 

 operculum, and it is provided with typical parietal muscles. The 

 distal group on each side is especially strong and it appears to me that 

 the part of the compensation sac immediately adjacent to the base 

 of the operculum into which these muscles are inserted, is somewhat 

 fascia-like, an arrangement which confirms the view that the muscles 

 function as divaricators " (Harmer, 1902). 



Operculum. — "The operculum, which may be more or less chitinized, 

 is often almost membranous and not distinctly separated from the 

 compensation-sac." 



"Lyrule and cardelles resemble in form and position the hinge 

 teeth in many Smittina species, but they can not be compared with 

 these, as they are placed outside the operculum." (Levinsen, 1909.) 



