MUSEUM OF COMPARATIVE ZOOLOGY. 141 



cast of the chambers. The mouth is surrounded by a circle of about 16 

 rather long tentacles, bluntly tuberculated at the tip. Outside the circle 

 of tentacles extends a membranous disc with radiating and concentric 

 folds. 



This unique specimen was dredged in 324 fathoms off' the Florida reef. 



Genus Pliobothrus Pourt. 



Tissue more compact than in Millepora ; larger pores scarcer, smooth, 

 without any rudiments of septa ; smaller pores tubulated ; coenenchyma 

 with still finer linear pores. Form generally branching regularly. Differs 

 from Heliopora by its tissue not being prismatic. I refer to this genus two 

 species described by me as Heliopora tubulata and carinata (Bulletin Mas. 

 Comp. Zool. No. 6), and a third species. 



Pliobothrus symmetricus Pourt. 



Corallum ramose, rising from an incrusting base and a short trunk, 

 branching into a regular semicircular flabellum. Branches not much 

 divided, cylindrical, and a little flattened and expanded at the tip, which 

 is blunt and rounded. The tendency in branching is towards considerable 

 symmetry between the two halves of the flabellum. Three kinds of pores ; 

 very small, linear, over the whole coenenchyma; larger tubulated, with very 

 minute aperture when unbroken, and larger round or oval ones scattered 

 irregularly. Internal structure somewhat like Millepora, but much coarser. 

 Larger pores interrupted by few but massive tabula?, but communicating 

 laterally with other canals. 



This species is much larger and more branched than Heliopora lubulata, 

 and has shorter tubes to the pores. 



Color gray ; height 1^ inches; spread about three inches; diameter of 

 branches 0.G3 of an inch. Not rare between 100 and 200 fathoms off' the 

 Florida reef. 



Cambridge, Mass., December 8, 18G8. 



T deeply regret the absence of Count Pourtales from Cambridge at 

 this moment, even though his return to the field of observations which 

 has already yielded him such a rich harvest cannot fail to benefit 

 science in the highest degree. My regret arises chiefly from the fact 

 that he is thus prevented from reaching some conclusions which belong 

 to him by right. But the very day he started on his third journey of 



