578 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 



the hiru-cr. In fully cstulilishcd colonies the tentaele.s appear pi-actitally dieyclic. and are both 

 eutocu'lic and exoeielie in position; the former are the more internal, and correspond with the sei)ta 

 below, while the exotentaeles have no eorrespondini;' septum beneath. Usually the tentacles are 

 shortly conical, with a white opaque apical swellinj;'. not t'ormiui;- a distinct knob; at othei' times 

 they are narrow(M'. and more elongated, and the apex appears as a sjiheroidal knob. White, oval 

 or irregular nematocyst batteries, varying in size and arranged circularly, occur all over the 

 surface. On full expansion the tentacular walls may become invohcd in the discal tissues, to such 

 an extent that they appeal- as mere circular patches, l)arely distinguishable except for the pi-esence 

 of the denser apical region. Under certain conditions some of the tentacles have l>een found 

 couipletely introverted, oval apertures indicating their ])osition externally; under these circum- 

 .stances the disk appears as a smooth, naked, tlattencKl expansion, not sharj)ly n-.arked off from 

 the col num. 



The disk is verrucose, usualh* depressed, and ridged and grooved radiately, the grooves cor- 

 responding w'ith the luesenteries. The radiating areas are larg<M- and smaller, but the alternation 

 is not always i-egular; whei'e the discal system is elongated the areas become more transverse. 

 Numerous oral apertures occur along the discal depressions, and vary nuuh in size. Some may 

 have a longer diameter of 2.5 nuu.; the smaller are circular, but others are oval, the gi-eater 

 diameter being always along the larger discal axis. The mouths are usually open, allowing the 

 .stomodfeal wall to be seen, and often occur on a distinct raised peristome; when closed they 

 appear as mere slits in the disk. In the condition of partial ex])ansion the apertures occur at 

 intervals of about half a centimeter, the numl)er varying, of course, with the size of the colony. 



The stomoda'iuu is sharply marked off fn^u the disk, no rounded lips intervening; under 

 certain conditions it may be partly extruded. The walls are very deeply ridged, as many as 

 seven or eight, or even ten, ridges occurring on each side. They can be seen to correspond with 

 the line of attachment of the mesenteries on the internal side, and thus represent the number of 

 complete mesenteries associated with each stomodanim. 



During full expansion the polypal tissues are semi-transparent, and the internal mesen- 

 teries can be seen through. In one case seven pairs were found to reach the stomoda?um, and in 

 another ten pairs; in one colony the numbers of perfect mesenteries around four oral apertures 

 were 12. l.i. 17, and 20, respectively. The course of the mesenteries from th(> periphery towards 

 the stomoda'um, as seen through the disk, is mostly at right angles to the calice wall. In so?ne 

 pairs the course is curved, while in those most distant from the oral aperture it may form an 

 •obtuse angl(>. The mesenteries are also seen extending the whole way down the edge-zone, as in 

 the column wall of an A<'tinian. 



The color is very variable, even in colonies living within the same area. Yellowish brown, 

 as in so many other corals, is the fundamental color, and upon this may lie sup(>rposed an 

 ectodermal opai[U(> white or green. The eolunni wall generally exhibits only lighter and darker 

 shades of brown, due to the internal zooxanthelhe; and sometimes the whole colony- may be of this 

 character. The disk in most cases is lighter than the rest of the colony, often an t)paque pale 

 gi"een; the color here appears (juite superiicial. as if ])ro(luced by some dense, opaque white or 

 pale green ectodermal deposit. The rows of verruca' also may be opaque white, while the ground 

 color is green. A similar appearance, though somewhat less dense in character, may occur on 

 the upper region of the colunui wall. In numerous colonies at Bluetields the coloration was 

 distributed in darker and lighter irregular patches. WIkmi the polyps are fully distended, the 

 distinctive colors largely disappear, the tissues becoming a p ile brown, and more or less trans- 

 parent. The tentacles are always colorless and transparent, but more opa(|ue over the lateral 

 urticating areas, and entirely so at the apical swelling. .V dull, white ring may surround the 

 oral cone. 



Colonies have been collected of which the gastro-coeloraic cavity contained numerous free 

 swimming larva\ readily seen through the partly transparent tissues. Many also circulated 

 freely within the tentacular cavities. Most of the larva' were elongated, with a light broader 

 pole, directed forward in progression, and a dark luown. narrow, jxjsterior j)ole. At times they 



