Bryozoa. 439 



the frontal area is wholly membranous, and the var. catenularia 

 in which the membranous area is greatly reduced. The latter, which 

 is widely spread in the arctic seas, often forms a more or less irre- 

 gular dendritic pattern. 



A single colony of the var. catenularia on a stone. 



Station 63. Stormbugt, 20— 40 m. 



Membranipora (Callopora) craticula Alder 



Membranipora lineata 1, forma craticula Smitt, op. cit. 1867, pp. 363 



—64, pp. 390—93. 



— craticula Hincks, Brit. Marine Polyzoa, p. 147, pi. 19, 



fig. 7. 



— — Levinsen, Mosdyr, op. cit. p. 60, Tab. V, figs. 



4—6. 

 Callopora — Norman, op. cit. 1903, p. 589, pi. 13, fig. 3. 



Membranipora craticula Osburn, Bryozoa of Woods Hole Region (Bull. 



Bureau Fisheries, vol. 30, 1910, p. 229, pi. 23, 



figs. 32, 32 a, 32 b). 

 (Pi. XIX, figs. 4, 5, 6, 7). 

 In my paper on the Danish Bryozoa (Mosdyr) I have pointed 

 out that in this species an independent avicularium appears which 

 has been figured, but not mentioned, by Hincks. These avicularia 

 are most conspicuous in the free margin of the colony; especially 

 when we regard a young disciform colony, we find them in the 

 whole circumference of the latter, placed in a number of 1 — 7 along- 

 side each other, each such series being separated from the next 

 one by a various number of zooecia. We may discern two different 

 sizes, large ones, in which the avicularian beak is surrounded by a 

 broad, somewhat convex area (fig. 4) and small ones from which the 

 ooecium belonging to a subjacent zooecium is formed (fig. 6). Such 

 a small avicularium is easily discerned from a superficial or inde- 

 pendent one seated on an ooecium, in that that it does not rise 

 from the top of the ooecium, but is only placed distally to the latter, 

 and when a colony is regarded from the basal surface it is easily 

 recognised by means of its small independent chamber provided with 

 a vertical distal wall and with pore-chambers. 



In the colonies examined the length of the ?ooecia varies. The 

 membranous area is surrounded by 14 — 19 somewhat flattened acu- 

 minate spines. Besides the well-known avicularium placed proxim- 

 ally to the membranous area (in zooecia with ooecia seated on the 

 top of the latter) there is mostly, in a various number of zooecia, 

 found one or two small lateral avicularia with the mandible directed 



