DENDRONOTUS ARBORESCENS. 



There are six or seven pairs diminishing in size towards the tail, which does not extend far 

 beyond them. In fine old specimens there are also smaller intermediate tufts. The anterior 

 pairs have four or five principal branches, which are divided and subdivided into numerous 

 delicate points. The posterior ones are less branched. Foot very narrow, linear, rounded 

 in front, the sides thin, and adapted for clasping. The heart forms a large swelling between 

 the first and second pairs of branchial tufts. It pulsates about seventy-six times in a minute. 

 The eyes are placed on the sides a little below the tentacular sheaths, and are very small. 



The young are very pale, and the spots exceedingly delicate : in this state the digestive 

 system is distinctly seen extending nearly the whole length of the body, and giving off 

 branches into the arborescent tufts and tentacles. 



When fully developed this is a splendid animal. It is subject to much variation in 

 colour, which has given rise to some spurious species. Occasionally we have met with an 

 individual perfectly white and transparent, showing the coloured viscera within. This we 

 take to be the Tritonia lactea of Mr. Thompson. Another beautiful variety, which we 

 formerly described under the name of Trit. pulchella, is much smaller, and of a uniform 

 pale rose-pink, with yellow tubercles. The Trit.felina, also described by us in the e Annals 

 of Natural History,' may possibly be another variety, but as there are some little differences 

 of form and consistence, we prefer keeping it apart at present. 



These molluscs crawl but slowly on a plain surface, but on corallines they move with 

 graceful facility, their tree-like plumes waving at every turn. Frequently, clasping the 

 coralline with only a small portion of the foot, they will remain suspended by it, moving their 

 bodies about in all directions. 



Dr. Grant has given a curious account of sounds emitted by these animals, which he 

 conceives to proceed from the action of the jaws. Though we have frequently kept them 

 alive for several days together, we could never succeed in detecting any sound. It may pos- 

 sibly only be produced under peculiar circumstances. 



Dendronotus arborescens appears to have a wide range in the northern seas, extending 

 from Greenland to the shores of the English channel ; and it is again met with on the north- 

 east coast of America. 



Its spawn is deposited in the spring months, at which period large individuals may usually 

 be found among the rocks between tide marks. The young, however, occur all the year 

 round. The spawn is of a pale yellow or rosy colour, and is about twice coiled ; the ova are 

 arranged in a small cord doubling upon itself as in the spawn of Eolis painttosa, which this 

 greatly resembles, but is not quite so large. 



Fig. 1. D. arborescens, usual appearance. 



2. Light red variety. 



3. White variety, {Tritonia lactea, Thomp.) 



(The figures in this Plate have been inadvertently reversed.) 



