1922. No. 6. NLDIBRANCHFAUXAEN I DR0BAKSUNDET. 95 



Ae. glauca. (A. »S: H.I Bergh. 



Fig. 55 in text. 



New to the fauna of Norway. Was found in great numbers spawning 

 on the Zostera in the Halangs-poU during July and August 1919 and 20. 

 hi 192 1 it was not to be found in the Drøbak Sound. Length up to 50 

 mm. The colour never so red, the cerata never so vermicular and so flat as 

 stated bv A. & H. The colour of the liver-processes blueishgrey. The 

 green colour given in A. & H.'s picture of a specimen was never observed 

 in ours. The anatomy of this species was thoroughly examined and was 

 found to accord with previous observations. 



The egg strings were formed to be like long threads wound irregu- 

 larly round Zostera leaves. The species has never been observed in Norway 

 except at its spawning season. 



Genus 8. Favoriniis. Gray. 



Diagnosis of the genus in accordance with Bergh's (1882, p. 38). 



F. albus (A. & H.) Gray and F. branchialis (Müller! Bergh, which 

 have previously been described as two separate species prove to be varie- 

 ties of one species, which in this work has been called F. albus (A. & H.) 

 Gray. According to the strictest rules of priority the oldest name '' F. 

 brancliialis (MCller)" should really have been preserved as the name of 

 the species; my reason ibr not following this rule is that the white variety 

 F. albus is by far the commonest and is found in wider areas, and is 

 therefore more often mentioned in scientific literature than Müller's brown 

 \arietv „F. branchialis.'' A changing of the well known name F. albus 

 might therefore cause unnecessary confusion. 



In the Drobak Sound fauna there have been found a whole series of 

 intermediate colours between that of F. albus and F. brancliialis, and also 

 with regard to morphology no difference can be demonstrated. Thu^ the 

 teeth of the radula have in all specimens been found to be provided with 

 more or less definite denticles varying in number on each side of the 

 central cusp. 



During the winter 1919—20 the brown variety was strikingly frequent, 

 while in the autumn of 1921 there was a majority of white specimens. 



F. albus. (A. «S: Il.t Gray. 



Syn. F. brancliialis (MüllerI Bergh. 



PI. IV. Fig. 16—18. 



The white variety is new to the Kristianiatjord fauna. The brown- one, 

 previously described under the name of Acolis brancliialis, was possibly 

 found by Asbjørxsen (1854 p. 33). Fairly common. Mature specimens 

 found from 6 to 22 mm. Very varying with regard to colour ot the liver 



