MEMBRANirORA UNICORNIS. 155 



Zooecia large, oval, quincimcial, the margin granulated; 

 two spines on each side, near the top of the cell, the 

 lower pair showing in front of the ovicell. Ooecia sub- 

 cylindrical, smooth, with a strong rib just above the 

 margin, and bearing on their summit a large conical 

 avicularium. In the absence of the ovicell the avicu- 

 larium occupies the space at the bottom of the cell, 

 placed somewhat obliquely, and with the mandible 

 directed downwards. 



Colonies forming a rather coarse network, spreading in 

 subcircular patches. 



Range of Variation. There are occasionally two avicu- 

 laria at the base of the cell, which are placed one towards 

 each side. The zooecia are very uniform in size and 

 shape. 



Habitat. On shells, stones, Ascidians, &c., from shal- 

 low to deep water ; occasionally between tide-marks. 



Localities. Northumberland and Durham, old shells, 

 &c., frequent (Alder) : Balta Sound, between tide-marks 

 (C. W. P.) : St. Andrews, deep water (Dr. Mlntosh) : 

 Dogger Bank (T. H.). 



Geographical Distribution. Bohuslan, at greatdepths; 

 north of Spitzbergen, 6-50 fathoms (Smitt) : Greenland 

 {' Valorous ' dredgings) : Nova Zembla, 10-60 fms. (Nor- 

 denskiold) . 



Range in Time. Scotch Glacial deposits (Geikie). 



The avicularium in this species is large and massive, 

 and very decidedly suberect. The zooecia are of much 

 stouter build than in the following. The points of diffe- 

 rence between the two species are given in detail under 

 M. Dumerilii. 



