226 ROBERTSON [S^^] 



more or less striated. Radical fibers (fig. 2, /'._/".) developed mainly 

 upon the lower zoecia. 



The general habit of this colony resembles that of Scrupocellaria 

 The branches are very calcareous and erect, tending to flare outward. 

 They differ in this respect from the preceding species whose branches 

 curl inward. The number of zoecia in an internode is five or seven 

 as a rule, but there is considerable variation in this regard. Toward 

 the middle of a branch the number increases and 9, 1 1, or 13 are fre- 

 quently found. In one case 21 zoecia occur before the internode 

 bifurcates. On the lowest one or two zoecia of a colony, very small 

 lateral avicularia may sometimes be detected. Frontal avicularia ap- 

 pear only at infrequent intervals. The zoecium situated at the bifur- 

 cation of a branch usually possesses one below the aperture (fig. i, 

 ap.'). They appear occasionally upon other zoecia also, but no con- 

 stancy is maintained. 



This species is closely allied to M. duplex Smitt ('67), and to M. 

 jeffreysii Norman ('68), in its habit of growth. There are differences 

 in zoecial characters, however. Comparing pi. xix, fig. i, with pi. 

 XVI, fig. 25, Smitt ('67), it will be seen that this form differs from 

 M. duplex in its possession of opercula and spines, and in its lack of 

 avicularia. In comparison also with the original drawing, Norman 

 ('68), or with the figures given by Hincks ('80) it differs from M. 

 Jeffreysii in the number of spines, in the lack of avicularia, and in the 

 very different shape and inclination of the opercula. 



SCRUPOCELLARIA Van Beneden. 



SCRUPOCELLARIA SCABRA Van Beneden. 



(PI. XIX, figs. 3, 4.) 



Scrupocellaria scabra Hincks ('80), pi. vi, figs, i, 2. Hincks ('89), pi. xxi, 



fig. I. 

 Cellularia scabra Smitt ('67), pi. xvii, fig. 29. 



Habitat. — Growing entangled in seaweed. 



Local distribution. — Kadiak. 



Foreign distribution. — British coast ; North Sea ; Scandinavian and 

 Arctic seas ; Spitzbergen ; Davis Strait ; Greenland ; Reykjavik Har- 

 bor; Madeira. Form without vibracula : Greenland; St. Lawrence. 



The form of S. scabra which occurs in this collection lacks all traces 

 of vibracula. These structures are usually considered a characteristic 

 mark of this genus, nevertheless there seems to be sufficient reason for 

 placing it here, at least provisionally. 



