Cellepora andV&lythoa. 417 



sing structure in relief, radiating to the circumference (fig. 1, u) 

 from thesummit of the rostrum, which is thus grooved (fig. l,^(j), 

 forming a reticulation whose interstices are respectively perfo- 

 rated by a hole furnished with a circular membranous dia- 

 phragm (fig. l,v)', interstice irregular in size and form, sur- 

 rounded by three or more tubercles (fig. l,s). Ooecium 

 globular, smooth, overhanging the orifice, which is thus more 

 or less perpendicularized by it (fig. l,f). Avicularia lan- 

 ceolate, numerous, variable in size, situated in the angular 

 intervals left between the cells (fig. l^eeeee). Zooecium in 

 some parts covered with a minute calcareous granulation 

 (V pellicle), especially over the rostrum, not even excluding the 

 chitinous operculum of the orifice (fig. 1, t). Size of specimen 

 2^ inches in diameter from tip to tip of the longest arms ; 

 largest arm I inch long by half an inch in diameter at the 

 base. 



Hab. Marine. 



Log. Coast of Senegambia, West Africa. 

 Obs. The most striking characters of this species are its 

 asteroid form and spotted surface. Perhaps the colour of the 

 dark parts may arise from an excess of chitine, as it is gene- 

 rally transparent and diffuse. The zooecia composing them 

 do not appear to differ from the rest, excepting in their 

 prominence and more recumbent position, which, affording 

 the best view of the surface of the cell generally, has been 

 taken for the typical illustration (fig. 1, c) ; while those bear- 

 ing the ooecium (fig. 1,/) apjiear to be confined to the colour- 

 less and more erect forms, which, situated in the depressions 

 between the verruciform or coloured portions, are thus most 

 protected. There is, of course, a great variety in the minor 

 detail of the cell, as might be expected in an acervuline mass 

 heaped together irregularly; but the main characters are those 

 above given. Probably the cavity of the shell on which the 

 Polyzoon has grown was once tenanted by a hermit crab 

 {Pagurus) , which, from the inconvenience of the weight accu- 

 mulating around him, may have left it to the mercy of the 

 waves, whereby his commensalist perished, and the specimen 

 got to the shore, where it was picked up for preservation. 

 Conjecturing what must have been the size of the Par/urus, 

 compared with that of the shellj it does not seem unlikely 

 that the burden on the former, or its own increase in size, or 

 both combined, may have led to the desertion. Certain it is, 

 however, that the aperture of the shell would not have been 

 preserved if a Pagurus had not taken possession of its cavity, 

 since there is no shell-substance left in contact with the 

 zoarium for some distance inward from the orifice, although 



