BitYOZOA OF THE PHILIPPINE REGION 



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The operculum bears a wide, marginal sclerite thicker at the two 

 lateral bases. The two small occlusor muscles are inserted on the 

 inner border of this sclerite as it is easy to see on the operculum of 

 Petraliella chuakensis Waters, 1913, and Petraliella armata Waters, 

 1913, which we figure. 



Fig. 103. — Family Petraliidae Levinsen, 1909 



A. Petraliella dorsiporosa Busk, 1884. Distal pore chambers, tentacles, and 

 alimentary canal (dorsal side), X25. (After Marcus, 1921.) 



B, C. Petraliella vultur Hincks, 1882 var. armata Waters, 1913. B. Section 

 of tentacles near the base, X550, showing the two large fin-shaped tentacles with 

 long nuclei near the edge. C. Section, X85, through the zooecium showing the 

 tentacles, with two larger than the other. 



D. Petraliella elleri MacGillivray, var. biavicularia Waters, 1889. Structure 

 of the aperture with lyrule and cardelles, X50. (After Waters, 1889.) 



E. Petraliella dorsiporosa Busk, 1884. The distal lobes of the frontal shield 

 have nearly united on the distal side of the operculum. The compensatrix 

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

 (after Harmer, 1902); I, distinct lobes of the shield; av, avicularia of the frontal 

 shield; c, condyle; cs, distal portion of the compensatrix. 



F. Petraliella chuakensis Waters, 1913. Dorsal surface showing spaces for the 

 attachment of radicle tubes, X25. (B, C, F. After Waters, 1913.) 



G. Petraliella dorsiporosa Busk, 1884. Dorsal face showing the radicells. 

 (After Busk, 1884.) 



The operculum in opening operates around an axis without any 

 apparent lateral support, cardelles or condyles. The pseudolyrules 

 and cardelles which ornament the proximal border of the aperture, 

 have for their object the arresting and fixing of the operculum when it 

 is closed. The study of the interior shows often the two condyles 



