524 THE MICROSCOPE 



of the deep, found usually on old shells, an inch in height, 

 spreading itself fan-like, and of an ashy colour, deeply 

 divided in a dichotomous manner into narrow, thin, plane 

 segments, truncate at the end, formed of four or live series 

 of oblong cells, capped with a hollow, globose, pearly, oper- 

 culum seated between the spines, of which there is one on 

 either side of the circular aperture. The opercula are so 

 numerous, that they give to the upper surface the appear- 

 ance of being thickly strewn with orient pearls ; the under- 

 surface is even and longitudinally striated, the number of 

 striae corresponding to the number of rows in which the 

 cells are disposed. Dr. Johnston describes, amongst many 

 other British species, F. memhranacea, " a gauze-like incrus- 

 tation on the frond of the sea-weed, spreading irregularly 

 to the extent of several square inches." 



Dr. Perceval Wright discovered on the western coast of 

 Ireland a new genus of Alcyonidoe, which he named after 

 the well-known naturalist Mr. Harte, Rartea elegans, Plate 

 IV. 'So. 86. This polype is solitary, the body cylindrical, 

 and fixed by its base to the rock; it has eight ciliated 

 tentacles, which are knobbed at their base and most freely 

 displayed. It is a very beautiful polyzoon of a clear white 

 colour, and when fully expanded stands three-quarters of 

 an inch high.^ 



The fresh-water Polyzoa are peculiarly interesting ob- 

 jects for microscopic observation, from the very beautiful 

 manner in which they display their ciliated tentacula, set 

 upon a crescentic, horseshoe-shaped "lophopore." The 

 arrangement of the latter appendage has been the cause of 

 separating the fresh-water Polyzoa, from their marine 

 allies, into a sub-class ; the former being named Hippocrepa 

 (horseshoe-likej, and the latter Infimdihulata (funnel- 

 like). ^ The most striking form among the Hippocrepa is, 

 the Gri&tatella Mucedo —a wandering Polyzoon, capable of 

 moving freely through the water. It may be met with 

 during a great part of the summer in our ponds and streams, 

 amidst the stems and leaves of aquatic plants (Plate IV. 



(1) On a new genus of Alcyonidm. By Dr. E. Perceval Wright. Micros. 

 Journ. Science, vol. v. p. 213. 1865. 



(2) The rciadcr is referred to a valuable treatise on the structure and dassifi- 

 cation of this group by Professor AUnian, Monograph of the British Fresh- 

 toater Folyzoa, published by the Kay Society, 1S57. 



