570 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



distinct. Corresponding with the dentieulations of the costa?, the surface of the eolumii wnll is 

 strong!}' verrucose over its entire length, a larger series of verruciv alternating with a smaller, 

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

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

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

 tentacles, leaving onh- the middle region of the disk exposed. 



The tentacles are arranged in several series, })ut appear approximately dicyclic, an inner, 

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

 costa3 and septa. When fully expanded, the tentacles of the itmer cycle are seen to be situated at 

 slightly different distances from the center of the disk, indicating separate orders, but no hexameral 

 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 ti-ansparent 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 rast. 

 On partial expansion the tentacles are elongated, and the members of contiguous poh'ps may 

 intermingle; usually they ai"e short, stumpy, and rounded at the apex. 



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

 radiating ai-eas, alternating with the internal attachment of the mesenteries. They exhiliit an 

 approximate cyclical arrangement. In the more circular polyps six radial ai-eas can be made 

 out, extending as far as the stomodieum, and alternating with the.se may be one, three, or five 

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

 more than six pairs of radii are seen to reach the stomoda?um. During partial expansion the 

 disk is deeply depressed, but on full expansion becomes strongly convex, extending abo\e the 

 tentacular zone in some cases as much as 5 mm. The diameter of the disk of an average, simple 

 polyp is about 5 mm. The peristouie may be much elevated, and the mouth at the apex is 

 elongated. The stomodteum 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 ct)loiiies varies from a light, clear, yellowish green to almost ))lack, the 

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

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

 verrucw, but the more general coloration is due to the presence of zooxanthclhe in the 

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

 opacity occurs around the upper mai-gin 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 polj'ps; 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 fi.ssiparity results in two practically equal polyps, but 

 in most instances one is larger than th(> other. During the earlj' 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 thev separate further 

 and further below; the skeletal tissues also gi-ow inward from above downward, until the 

 mesenterial loculi of each polyp liecome separated all the \\ay. Instances occur in decalcified 

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

 tentacles, and column, Init below they apper as a simpl(> 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. 5Ub. 



