NATURAL HISTORY OF THE QETfUS DERO. 



93 



better course open than to entirely reject it. Up to the present 

 time the name is occasionally used on the Continent ; but as the 

 worm designated may be any one of three species at least, and as 

 no clear definite description has yet been given of any of these in 

 particular under the name in question, this cannot be used as an 

 argument against the course proposed. 



In acknowledgment of Miiller's work, I have attached his own 

 name to the last new species discovered. 



The name by which the genus is now known was bestowed upon 

 it by Oken(20) in 1815, and the species described by Eosel dis- 

 tinguished as Dero furcata, Miiller's appellation being retained 

 for the other species. This was apparently the extent of Oken's 

 knowledge of the genus, as his figure was taken from Miiller, 

 and his diagnosis is as scanty as possible. 



Dutrochet (9) rediscovered the genus, and being ignorant of 

 the work of earlier writers, renamed ib Xantho^ remarking that it 

 appeared either not to have been observed before or to have 

 been confounded with Nais. He also described the branchial 

 funnel as an organ of progression and retrogression and of pre- 

 hension ; the branchial processes being spoken of as veritable 

 non-articulated limbs, resembling the feet of cephalopodous 

 MoUusca and the arms of the polyps ! The number of branchial 

 processes is given as ten in one species and six in another, 

 to which the names Xantho decapoda and X. hexapoda are respec- 

 tively given. As the figures which accompanied the original 

 paper appear to have been lost, any attempt to identify Dutro- 

 chet's species must be mere guesswork. 



Blainville (1) gave a somewhat unintelligible account of two 

 species, named Nais digitata and N. decapoda. The former is 

 credited with the possession of six pairs of fleshy lobes, the 

 latter with five, reference being also made to a drawing in the 

 * Encyclopedic Methodique ' of a species with no less than eight 

 pairs. Having had an opportunity of examining the latter work, 

 I found that the plate in question is merely a replica of Miiller's 

 (18) ; while the peculiarly unmethodical character of the arrange- 

 ment of the text renders any search for the article referring to 

 the figures hopeless. However, as none of Miiller's figures show 

 more than four pairs of lobes, Blainville has evidently interpreted 

 them wrongly. 



Blainville (2) in a second article in the ' Dictionuaire des Sciences 

 naturelles ' and a writer in ' Rees's Cyclopaedia ' (23) quoted from 



LINN. JOUllN. — ZOOLOGY, VOL. iX. 8 



