570 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



distinct. Corresponding with the denticulations of the costse, the surf ace of the column wall is 

 strongly verrucose over its entire length. a linger series of verrucse alternating with a smaller. 

 the latter not always extending as far upward as the tentacular zone. On full expansion the 

 verruca' are oval shaped, and arranged in single rows over each mesenterial interspace. During 

 full retraction the column wall is overdrawn within the calice, so us to completely hide the 

 tentacles, leaving only the middle region of the disk exposed. 



The tentacles are arranged in several series, hut appear approximately dicyclic, an inner, 

 larger cycle corresponding with the larger costse and septa, and an outer, smaller with the small 

 eosta' and septa. When fully expanded, the tentacles of the inner cycle are seen to he situated at 

 slightly different distances from the center of the disk, indicating separate orders, but nohexameral 

 or any other regularity can be established. In preserved colonies the tentacles appear as two 

 rows of short processes around the margin of the column. The total number may vary from 

 about thirty to sixty, according to the size of the polyp; thirty-six were present on a medium-sized 

 polyp. 



The tentacular stem is finely tuberculated, bearing white urticating spots, and a rounded, 

 thickened area occurs at the apex, rarely appearing knob-like; otherwise the walls are very deli- 

 cate and transparent on expansion. Sometimes the tentacles, even during full expansion of the 

 polyp, are shrunk so that they appear darker in color, and the apex is broader than the rest. 

 On partial expansion the tentacles are elongated, and the members of contiguous polyps may 

 intermingle; usually they are short, stumpy, and rounded at the apex. 



The surface of the disk is finely verrucose, the verruca 5 being oval and arranged along the 

 radiating areas, alternating with the internal attachment of the mesenteries. They exhibit an 

 approximate cyclical arrangement. In the more circular polyps six radial areas can he made 

 out, extending as far as the stomoda?um, and alternating with these may be one, three, or rive 

 shorter radial areas, the number being inconstant even in individual polyps. In larger polyps 

 more than six pairs of radii are seen to reach the stomodseum. During partial expansion the 

 disk is deeply depressed, but on full expansion becomes strongly convex, extending above the 

 tentacular zone in some cases as much as ."> mm. The diameter of the disk of an average, simple 

 polyp is about 5 mm. The peristome ma}- be much elevated, and the mouth at the apex is 

 elongated. The stomodamm is colorless, and during full expansion is seen distinctly through the 

 transparent tissues of the disk; slight ridges and furrows are present, usually four to six on 

 each side. 



The color of the colonies varies from a light, clear, yellowish green to almost black, the 

 lower portion of the column being somewhat lighter, owing to the white corallum showing 

 through. A dark pigment is sometimes arranged in small oval patches, corresponding with the 

 verruca', but the more general coloration is due to the presence of zooxanthelhe in the 

 endoderm; sometimes the disk shows a light green iridescence. In some instances a thin white 

 opacity occurs around the upper margin of the column, opposite the large tentacles. 



Asexual reproduction takes place by fission. Two or more oral apertures on an elongated 

 disk are the first indications of the formation of new polyps; later the tentacular zone and a 

 septum from each side grow inward and complete the separation into two polyps, which remain 

 united only peripherally. In some cases tissiparity results in two practically equal polyps, but 

 in most instances one is larger than the other. During the early stages two oral apertures are 

 found close together, each smaller than usual. 



Stages in the separation of the fissiparous polyps can be best made out in decalcified portions 

 of colonies. The polyps first divide superficially, and as growth continues they separate further 

 and further below: the skeletal tissues also grow inward from above downward, until the 

 mesenterial loculi <>f each polyp become separated all the way. Instances occur in decalcified 

 colonies in which the polyps are wholly separated above, each with its oral aperture, system of 

 tentacles, and column, but below they apper as a simple polyp. In a portion of a colony 

 decalcified twenty-two oral disks were counted, but only sixteen distinct aboral disks. The 

 process of fission in this species has been more fully described on p. 508. 



