Polyzoa of Queen Charlotte Islands. 15 



[Normal : Arctic and northern seas ; Britain, France (south- 

 west), Mediterranean, Florida, Zanzibar, Australia, New Zea- 

 land, &c. Var. Californica^ California.] 



Microporella ciliata, form vihracuUfera *, n. 

 (PI. XVII. fig. 2.) 



Avicularium replaced by a very tall membrano-chitinous 

 vibraculoid process, situated on a rather large mound or 

 swelling, the beak elevated at the sides and somewhat deeply 

 notched or channelled at the extremity. 



This is in many respects the most remarkable form which 

 Dr. Dawson's dredgiugs have yielded. It occurs abundantly 

 and in company with the normal M. ciliata and several inter- 

 esting varieties. 



I have already discussed (in the paper referred to) the 

 curious morphological change which the avicularian organ has 

 undergone in this variety, and its significance as illustrating 

 the relation between the two appendages (avicularium and 

 vibraculum). The mandible of the avicularium is frequently 

 slightly elongated, and projects a little beyond the anterior 

 extremity of the beak. In the present variety this elongation 

 has been carried very much further, and at the same time a 

 narrow chitinous expansion seems to have been developed 

 along each edge of the setiform process thus formed. In this 

 way a tall vibraculoid organ has taken the place of the normal 

 mandible. The beak survives ; but it too has undergone a 

 certain amount of modification, tending to secure freer play for 

 the movable seta. In general character the present variety 

 agrees entirely with the ordinary forms of M. ciliata. 



A glance at the three varieties represented on PL XVII. 

 (figs. 1, 2, 3) will suffice to show what an amount of super- 

 ficial difference there may be within the limits of one and the 

 same species, and may well suggest those structural elements 

 which should have most significance with the systematist, as 

 indications of genetic affinity. 



Mtcropo)-ella ciliata, form urnhonata, n. (PL XVII. fig. 1.) 



An umbonate process placed on each side of the orifice. 

 Below the inferior margin a massive mamillary rising, 

 which, when fully developed, conceals the pore. The entire 

 surface thickly covered with rather large punctures, which are 

 sometimes arranged in radiating lines. 



Loc. Dolomite Narrows, on stone. 



* See a paper by the author '•' On certain remarkable Modifications of 

 the Avicularium in a Species of Polyzoon ; and on the Relation of the 

 Vibraculum to the Avicularium " (' Annals ' for January 1882, p. 20). 



