1889.] NATURAL SCIENCES OF PHILADELPHIA. 121 



greatest part of their extent, are yet free above. Duchassaing 

 and Michelotti in their paper of 1860 describe a form under this 

 name which differs somewhat from the original type species, and 

 is probably to be considered, as Andres has clone, a distinct form. 

 In their later paper they make this form identical with a form they 

 name Palythoa mammillosa, a name taken from a second imper- 

 fectly characterized form mentioned by Ellis and Solander. In 

 fact so much confusion is introduced by Duchassaing and Mich- 

 elotti as to render it very difficult, if not impossible, to ascertain 

 what forms they are really describing. 



Under the circumstances I have thought it well to retain the name 

 which accompanied the specimens, and trust that the following 

 description will sufficiently characterize them to allow of the identi- 

 fication in the future. 



The polyps are grouped together in small masses, and project 

 decidedly above the surface of the ccenenchyme. Their height 

 measured from the lower surface of the ccenenchyma is 1-2 cm. 

 and their breadth, measured at the summit, about 0*7 cm. in the 

 fully grown individuals. The polyps and ccenenchyma are densely 

 in crusted with particles of sand and other foreign bodies, and are of 

 a grayish sandy color, sometimes deepening to a rust color. 



Upon the outside of the column is a rather thick cuticle, but I 

 was not able to discover whether or not a layer of mesoglcea inter- 

 vened between this and the ectodermal cells. The outer portion of 

 the mesoglcea for about half its thickness has imbedded in it foreign 

 bodies, and when decalcified is fenestrated by the numerous cavities 

 previously occupied by them. The internal portion of the layer 

 presents the structural features found in other Zoanthidse, but it is 

 to be noticed that foreign bodies occur in the so-called " nutritive 

 canals" or lacunar The sphincter muscle is imbedded in the mesr 

 ogleea, is single, and consists of a single row of cavities containing 

 muscle fibres. 



The tentacles are arranged in two rows and are apparently fifty- 

 six in number in the specimens examined. Their outer muscular 

 layer is weak and the mesoglcea is homogeneous except upon the 

 outer face of the tentacles where it contains a number of granular 

 cells similar to those occurring in the column mesoglcea in this and 

 other forms already described. Zooxanthellre occur in the ectoderm. 



The ectoderm of the disc is peculiar. It consists of high much- 

 vacuolated cells which contain, like the ectoderm of the tentacles, 



9 



