696 Reports on the Zoological Collections made in Torres Straits, 1888—1889. 



moderate thickness. Polyps large, not crowded, of rounded contour. The whole 

 surface is incrusted with calcareous particles. About twenty capitular ridges. 



Colour. — Grayish-white in spirit specimens. 



Dimensions. — Diameter of polyps about 9 mm. The colonies in the specimens 

 before us average about 50 cm. by 40 cm. 



Locality. — Reefs, Torres Straits. 



men "i 



"We have doubtfully referred this species to P. coesia, which was collected by 

 the United States Exploring Expedition at Fiji. The size and disposition of the 

 polyps are fairly similar in the two forms ; but the coenenchyme of ours is less 

 convex. From the specimen figured (PI. lxi., 

 fig. 14), it would seem that the colony divides 

 after it has attained a certain size. 



Bodij'tvall. — In its anatomy this species is in 

 most respects very similar to that of P. Jcochii. 

 The ectoderm is covered by a thin cuticle, and 

 is continuous. It contains nematocysts and 

 zooxanthellse. Incrustations are even more 

 numerous than in P. kochii, and they penetrate 

 the mesogloea, which separates the polyps to a 

 greater extent than in that species. They con- 

 sist of sponge and ascidian spicules, foramini- 

 fera, &c., as well of great numbers of grains 

 of sand. Lacunae of variable size are very 

 numerous in the mesogloea. In some cases a 

 great number of these lacunae placed close to- 

 gether form a sort of spongy or vesicular sheath 

 round an individual polyp. Nematocysts are 

 commonly to be met with in the lacunae. The 

 endoderm is not very well preserved, but it 

 appears to form ridges between the mesenteries, 

 rather than a thin uniform layer as in P. Jcochii. 

 The endodermal muscular layer appears to be 

 well developed; 



Sphincter muscle. — The single mesogloeal sphincter is a strong one. 



Disc and tentacles. — The disc and tentacles are veiy similar in structure to 

 those in the last two species, the ectoderm being remarkably thick. 



(Esophagus. — Nematocysts are very numerous in the ectoderm of the oesophagus. 

 There is a well marked groove. 



Mesenteries. — The arrangement of the mesenteries is brachycnemic. The 



lac. '-'. 



Fig. 2. — Pahjthoa coesia {"i). Transverse 

 section of body- wall. 



