154 A. E. Verrill — Bermudian and West Indian Reef Corals. 



secondaries, and those of each cycle are successively narrower and 

 thinner ; all are nearly straight and seldom united. The proximal 

 half of the inner edge is nearly perpendicular, thus producing a 

 deep central pit. The columella is small and papillose. 



The polyps are but slightly exsert ; the tentacles are small, short, 

 cylindrical, or clavate ; they form several circles, and appear some- 

 what scattered, those of successive cycles being in different circles 

 and decreasing in size. 



But they are not bilobed, nor trilobed, as Agassiz and Pourtales 

 supposed.* This appearance is due to a smaller one standing on one 

 or both sides of a larger one, and close to it. 



The general color in life is dull gray, yellowish gray, ocher-yellow, 

 or rusty brown, sometimes tinged with a purplish rosy tint ; the 

 polyps are paler, with the lips and tips of the tentacles whitish. 



This species, which is abundant at the Bermudas, is more hardy 

 than most reef corals, for it can live and grow well in shallow water 

 on mud flats, where it is laid bare by nearly every tide, and where 

 most other corals would be smothered in the mud, though S. siderea 

 and some forms of Isophyllia fragilis are usually found with it in 

 such places. 



It is often partly buried in the white calcareous mud of the flats, 

 and yet seems healthy there. It is also abundant in the small, shal- 

 low pools left on the flats by the tide. But it is equally common on 

 the reefs, where it often grows larger. It is also found well grown 

 in Harrington Sound. 



Exposure to the dry air, or even to the hot sun, for an hour or so, 

 does not kill it, if it be wet beneath. Probably its porosity enables 

 it to absorb sufficient water to prevent drying up. 



It is equally common on the Florida reefs and flats, and through- 

 out the West Indies to South America and Colon. 



The decidedly smaller size of the calicles, fewer septa, and the 

 conspicuously larger primary and secondary septa serve to distin- 

 guish this species from S. siderea. 



But it varies considerably in all these characters, so that some 

 specimens may occur that seem almost intermediate between the two 

 species. In all such cases the average condition of the full grown 

 calicles must be considered as of primary importance. 



* The observations of Prof. L. Agassiz on the polyps of this genus, in 1850, 

 and his figures in "Florida Eeefs," pi. xv, figs. 1-7, relate to S. radians. In my 

 note on this subject (these Trans., x, p. 554, 1900), I referred to it under 

 S. siderea. But my studies of the polyps included both species. They are very 

 similar, but S. siderea has larger polyps and more tentacles. 



