242 



LOWER INVERTEBRATES. 



the colony a very graceful appearance. Occasionally the species are found in the 

 greatest abundance, flumes leading to tide-mills being especially favorable localities. 



These forms are most favorable for studying the motions 

 of the avicularia. 



The second super-family, the FLUSTRINA, embraces 

 flattened forms vfith quadrate cells and an even surface. 

 Very frequently the col- 

 ony is reduced to a mere 

 incrusting scale upon 

 stones or sea-weeds. Our 

 most common forms be- 

 long to the genus Mem- 

 bra?iipora, which is sepa- 

 rated from Lepralia in 

 having the anterior cell- 

 wall membranous instead 

 of calcareous, as in that 

 genus. The edges of the 

 cells are ornamented by 

 long and slender spines, the numbers and shape vary- 

 ing according to the species. The species of Flustra 

 assume a branching form, the branches being broad 

 and flat. 



The ESCHARINA are Polyzoa with a lateral 

 opening to the quadrate or half-oval cell. The first 



Fig. 241. — Bngula turrita. 



Fig. 242. — Membra7iipora pilosa; a, por- 

 tion of a colony; b, side view of a single 

 cell; c, a single polypidea; 11 enlarged. 





Fig 243 —Lepialia 



f a m i 1 y, 



the EscHAEiPOEiDJs, has the cells rhomboid 

 or cj'lindrical, while the opening is semi- 

 circular, with the anterior margin split or 

 perforated witli a median pore. In the 

 Mykiozoid^ we have erect forms, with 

 more or less cylindrical branches, the pos- 

 terior margin of the mouth of each cell 

 being exca\'ated. Myriozoum subgracUe, 

 which we figure, is found north of Cape 

 Cod. The Eschaeid.^ have the principal 

 mouth of the cell semicircular or round, 

 the secondary being reduced to accom- 

 modate the occasional avicularia. The 

 colony may be either in the form of round 

 branches or of broad, flat divisions, the cells 

 occupying the opposite sides. The Dis- 

 copoEiDJE have oval or rhomboid cells, with 

 semicircular mouths, the posterior mar- 

 gins of which are armed with one or more 



spines. 

 In the CELLEPORIISrA the colony is calcareous, the cells being rhombical or 

 oval, and the mouth is terminal. Two well-marked families exist. The first, Celle- 



