POLYPS AND CORALS. 97 



low down on the sides of the branches. Septa twelve, 

 quite distinct, though narrow, one of them joining the 

 columella, which is usually distinct, but low down in the 

 cell ; surface of coenenchyma rough, thickly covered with 

 rather coarse spinules. 



Hawaiian Islands. W. T. Brigham. 



This species is nearly allied to P. aspera.by the struc- 

 ture of the cells and surface of the co3iienchyma, but is 

 remarkable for its peculiar frond-like branches, destitute 

 of distinct verrucas. It is possible, however, that it may 

 eventually prove to be only an extreme variety of that 

 species. P. informis Dana differs in its irregular mode 

 of growth and in the absence or rudimentary condition 

 of the septa. 



POCILLIPORA NOBILIS Verrill. 



Pocillopora verrucosa (pars) Dana, Zooph., p. 529, Plate 50, fig. 3, 

 3a, 1846 (non Lamarck ; Edw. and Haime). 



Pocillopora nobilisVerrill, Bulletin Mus. Comp. Zoology, p. 59, 1864. 



Corallum firm and dense, forming large round-topped 

 or hemispherical clumps, often a foot or even eighteen 

 inches in diameter. Branches nearly equal in length, 

 separated by regular intervals of .4 to .5 of an inch, 

 elongated, often nearly round, .6 to .75 of an inch in 

 diameter, regularly forking and not enlarged at the ob- 

 tusely rounded ends ; in other cases, even in the same 

 specimen, dilated at the ends to a breadth of two or 

 three inches and more or less plicated. Summits of the 

 branches generally strongly verrucose, the verrucas simi- 

 lar to those of the sides, but usually smaller and more 

 crowded. Lateral verrucas very numerous, rather 

 crowded, the intervals being usually less than their di- 

 ameter, small, regular, spreading obliquely, or even stand- 

 ing at right angles to the surface, tapering and somewhat 

 rounded at the end, but angular and containing but few, 

 quite large cells. Between the verrucse the cells are 

 rather large, numerous, usually less than half their own 

 diameter apart. Septa but little developed, very narrow, 

 usually indistinct, or wholly obsolete. Columella very 

 small or wanting. Surface of the coeuenchyma regularly 



COMMUNICATIONS OF ESSEX INSTITUTE, VOL. VI. 13 NOV., 1869. 



