122 



very distinctly marked transverse Ix-ll almost midway across the frontal surface 

 of the oa>cium. The jiart of the ooecium lying proximally to this is furnished 

 along the middle with a narrow ridge. This cryptocyst-hridge must undoul)tedly 

 have arisen from a fusion of two triangular lamina> like those we have described 

 in Coluinnaria borealis. 



Family Flustridae. 



The zoa'cia slightly calcified, with an aperture whicii occupies Ihe whole 

 frontal surface, or at any rate its largest pari. Occasionally there is found a 

 secondary cryptocj'st. The distal wall is always provided with a varying number 

 (1 — 13) of small, uniporous rosette-plales, and such also appear as a rule on the 

 side walls, which only in a few cases are furnished with mulliporous rosette- 

 plates. Vicarious or independent avicularia. The owcia are endozocccial and immer- 

 sed, generally in ordinary zooecia, occasionally in avicularia or kenozooecia. The 

 colonies are in a few cases incrusting, in most cases free frondose, more or less 

 richly branched, and with the fiee margin consisting of kenozoa^cia. 



As the family is defined here, the main weight is laid on the possession of 

 immersed orecia and vicarious avicularia, as well as on the slight calcification 

 and the large frontal aperture, and I have therefore also referred ^Meinbranipora' 

 fltistroides Hincks and M. serrata M. Gill, to this family: the latter species has 

 been considered by Waters also as a Fliislnt. In conformily lo the above defini- 

 tion of this family, I have been obliged to separate out a number of species, 

 which partly have external ooecia, partly dependent avicularia. »F/Hs/r«« militaris, 

 ^Fl." irassd, F/.o dissimilis and »F/. < nobilis are Ihus referred to the /JiVe//ar/iV/oc and 

 ^Fl.'^ armata lo the Scnipocellariidae. Since however the ooecia and avicularia are 

 lacking in a number of species of this family as in most other families, and as 

 a number of Memhranipora species can have vicarious avicularia as well as a 

 quite uncalcified frontal wall, it is difficult to draw a sharp line between this 

 and the family Menihraniporidae. Memhranipora serrulata Busk is a species which 

 has been regarded both as belonging to Memhranipora and to Fhistra. According 

 loBusk"s original description it possesses immersed oct'cia, and if this were cor- 

 rect, il would have to be regarded as a Fhistra. but I have not succeeded in 

 finding ooecia in any of the specimens of this species, which our Museum has 

 from the Fvara Sea or from Greenland, nor are they found on Husk's original 

 specimens in the Brilish Museum. The species appears incrusting as well as in 

 free, bilaniinate growths, but it differs from the Fhistra species, known to meg'in 

 having mulliporous rosette-plates on the distal wall, as well as fully developed 

 marginal zooecia, and I therefore find it more natural lo look upon it as a Mem- 



