1898-1902. No. a] BRYOZOA. H 



area was from 0.26 to 0.3 mm. in length, from 0.2 to 0.26 mm. in 

 breadth. There were as a rule 2 or 3 spines on each side, and the 

 lateral avicularia were very often found. When boiled in potasium 

 hydrate, the mandibles fell off, and the hollow in the median avicularium 

 became visible. This hollow proved to be connected with the zocecial 

 cavity by from 2 to 5 pores. In the colonies fi-om N. Devon, the late- 

 ral spines had fallen off. The length of the area was from 0.33 to 

 0.39 mm., its breadth 0.26 mm. When the spines are absent, the spe- 

 cies may be mistaken for M. unicornis, var. armifera. JMorman has 

 pointed out, however, a good distinguishing mark; in armifera the point 

 of the mandible is directed downwards or outwards, while in arctica it 

 is directed upwards or inwards. 



13. Membranipora. unicornis, Flem., var. armifera, fliNCKs. 



1867. Membranipora lineata, forma americana, Smitt, Ofvers. Kgl. Vet. Akad. 



Ferh. 1867, pp. 366 & 400, PI. 20 fig. 31. 

 1892. Membranipora armifera, Hincks, Ann. Mag. Nat. Hist., Ser. 6, vol. 9 p. 155, 



PI. 8, fig. 4. 

 1898. Membranipora Sophice, var. armifera. Waters, Journ. Linn. Soc, vol. 27, 



p. 680, PI. 48, fig. 18- 

 1903. Callopora unicornis, var. armifera, Nokman, Ann. Mag. Nat. Hist., Ser. 7, 



vol. 11, p. 591, PI. 13, figs. 10 & 11. 



September 19, 1900, off Forvisnings Valley; September 20, 1900, 

 head of Gaase Fjord, 3—20 fath.; July 9, 1901, between Ren Bay and 

 Cape Land's End ; July 12, 1901, bay at Land's End, on algae; August 16 

 1901, Gaase Fjord, about 7 fath.; August 30, 1901, Gaase Fjord, 8 m. 



Norman, who has unravelled the synonymy of this form (1. c, 

 p. 591), looks upon M. armifera, Hincks, as a variety of M. unicornis; 

 and there is much to be said in favour of this view. 



In the typical M. unicornis, there are 2 spines on each side of the 

 upper part of the area. I have moreover once seen in a colony 

 from Bergen, instead of the one spine, a small laterally situated avi- 

 cularium. On the other hand no one has observed an avicularium on 

 each side in M. unicornis, while the appearance of two such is of fre- 

 quent occurrence in var. armifera. 



With regard to armifera, I refer the reader to Norman's excellent 

 description (1. c, p. 592). I have made some measurements of the fron- 

 tal area in the typical form, and in armifera. 



In a colony of M. unicornis from Bergen, the length of the frontal 

 area was 0.39 mm., its breath 0.26 mm. There was a form trom the 

 2nd Fram Expedition (August 30, 1901), in which the dimensions of the 



