MATTHAI— RECENT COLONIAL ASTR^ID^ 81 



in a simulated pali-crown. Columella formed of twisted trabeculse (e.g. Favia ehren- 

 hergi var. laticollis, Klunz.). 



In some specimens the corallite-rims are distinct, oval or circular as in the following 

 species, F. doreyensis. 



The specimen referred by Gardiner to a new species P. suvadivce is only an abnormal 

 skeletal variation of the present species. The much greater thickness of the perithecal 

 regions and the somewhat filled in appearance of the calices are doubtless due to 

 slackened growth under unfavourable conditions ; as Gardiner suggests, " it was probably 

 growing on the edge of a lagoon shoal and fell off into deeper water, the muddy bottom 

 of which was slowly killing it." It is remarkable that other Suvadiva specimens, cp. 

 Cyphastrea maldivensis, should also show the same type of modification. 



Polyps. (1) Both entocoelic and exocoelic tentacles present. (2) Stomodseal ridges 

 as thick as or thicker than broad, with sides either parallel or constricted at their bases 

 and inner surfaces somewhat flattened. (3) About ten principal couples of mesenteries. 

 (4) In the stomodseal region of polyp subsidiary couples of mesenteries about twice the 

 number of principal couples. (5) In same region of polyp, entocoelic pleats narrow, 

 unconstricted, undivided and not extending to middle of width of principal mesenteries ; 

 inner one-sixth of mesoglgea. thickened with a few narrow exoccelic pleats, remaining 

 part thin. (6) Mesenterial endoderm uniformly thin, except on each side of the inner 

 thickened region of mesoglgea where it is swollen. (7) Convolutions of mesenteries massed 

 together in inter-mesenteric chambers below stomodseum in the stomodseal region of polyp, 

 a characteristic appearance in transverse section is due to convolutions of subsidiary 

 mesenteries lying massed together as far inwards as the latter extend. 



Remarks. A. Polyps. Two of the typical polyps have each ten principal couples 

 of mesenteries, two of which are incomplete ; the remaining polyps have from nine to 

 twelve couples. The number of subsidiary couples varies from twelve to eighteen. The 

 exocoelic tentacles appear longer than the entocoelic ones. The terminal tentacular 

 battery is large and contains in its peripheral region closely packed nematocysts I, each 

 with from forty to fifty turns of the spiral ; among these are a few of type II b (mostly 

 thrust out of the batteries in the sections); below the nematocysts saccular nuclei of 

 varying size are crowded together. Sub-terminal batteries number from four to eight. 

 A thin longitudinal layer of muscle-fibres is clearly visible on the outer surface of the 

 tentacular mesoglsea. 



The stomodseum is oval in transverse section, with diameters measuring about 2 mm. 

 and 1'5 mm. ; its ridges are closely approximated to one another, but form deep and narrow 

 grooves between. Digestive vacuoles are frequently found in the peripheral part of each 

 ridge ; in this region nuclei, which have assumed the saccular appearance of those of the 

 tentacular and oral-disc ectoderm, are thickly crowded together, some extending even into 

 the central region of the ridge. Numerous nematocysts I are present in the lower half of 

 each ridge; the development of these in such large numbers may account for the 

 vesicular condition of the nuclei ; nematocysts III are rarely met with. The mesoglsea 

 is considerably thickened in the ridges. The ectoderm of the oral-disc is typical; along 

 its middle saccular nuclei (oval and elongated) are aggregated in diverging tracts of 

 SECOND SERIES— ZOOLOGY, VOL. XVIL 11 



