114 POTTSIELLA ERECT A. 



of a chestnut-burr. In the rivers they were found penetrat- 

 ing the mass of encrusting sponges, particularly Meyenia 

 Leidyi. 



These upright tubules are chitonous prolongations of very 

 irregularly inflated cells, resting in compact disorder upon the 

 supporting surface, crossed and connected in some manner not 

 yet intelligible, by meandering cylindrical rhizomes, some- 

 times of great relative length. These are mostly terminal and 

 simple, but are sometimes branched and frequently originate 

 in an indifferent lateral portion of a cell. The tubular pro- 

 longations are, of course, always single ; the invaginated 

 polyp retiring within the inflated portion of the cell. Septae 

 were, in a few instances, discovered in the rhizomes near their 

 insertion or connection with the inflated portion of the cells. 

 The upright portions of those cells which seemed to be least 

 matured were longer than those of their older neighbors, sub- 

 clavate or spindle-shaped and rounded at the extremities. 

 The others are cylindrical or slightly widening downwards 

 and shorter than the former by the invagination of the termi- 

 nal portion of the ectocyst. This has the effect of producing 

 the angular appearance of the orifice, so familiar in the older 

 species ; but while that is generally quadrangular, this has 

 frequently five or more sides. The younger cells aie nearly 

 transparent, but they darken with age and become somewhat 

 encrusted with adherent particles and overgrown by commen- 

 sal parasites, IJm7iias, Pyxicola, and the like. 



The polypides are shy, but fond of the light, and when 

 otherwise undisturbed will remain for a long time protruded 

 in the full glare of microscopic illumination. It can then be 

 seen that the lophophore is circular, without epistome, sup- 

 porting ordinarily twenty tentacles, taking the shape of a 

 claret glass and opening upwards. (Nineteen and twenty-one 

 tentacles have been doubtfully counted, while the above- 

 mentioned number is frequent ; P. Ehrenbergi is universally 

 stated to have but sixteen). A peculiarity of the tentacles 

 is the presence upon the outer median line of each, of a rather 



