242 



LOWER IN VER TEBRA TES. 



the colony ;i very graceful a]ii)earaiice. Occasionally the species are found in the 

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

 These forms are most favorable for studying tlie motions 

 of the avicularia. 



The second super-family, the FLUS'J'KINA, embraces 

 flattened forms with 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 3Iein- 

 bruiiipora, which is sepa- 

 rated from Lrjiraltd 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 ESCHAFJiSrA are Polyzoa with a lateral 

 ()])ening to the quadrate or half-oval cell. The flrst 



f a m i 1 }', 



- Buijnia tur 



i 



% 



Fl<;. 242. — Memhran'ipnra pilosa; a, por- 

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

 cell; c. a single polyjiiilea; II enlargeil. 



the EscHAKiPORii).!:, has the cells rhomboid 

 or cylindrical, while the opening is semi- 

 circular, with the anterior margin sjilit or 

 perforated with a median ]iore. In the 

 Mykiozoid^ we have erect forms, with 

 more or less .cylindrical branches, the pos- 

 terior margin of the mouth of each cell 

 being excavated. 3li/riozoum snbt/racile, 

 which we figure, is found north of Ca])e 

 Cod. The Escharid,k 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 

 tranches or of broad, flat divisions, the cells 

 a occupying the opposite sides. The Dis- 

 •opoRiD-*; have oval or rhomboid cells, with 

 '^ :^ semicircular mouths, the posterior mar- 

 gins of which are armed with one or more 

 spine? 



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

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



