64 Miscellanea Zoologica. 



which ought not to surprise us, for whenever organs, hecause of their 

 minor developement, become of slight importance in the economy 

 of the animal, and are about to be obliterated more or less entire- 

 ly from its anatomy, we find them to vary proportionably in their 

 forms. Such is the case with the exterior appendages of the Ari- 

 ciad^e, a small family which intervenes to smooth the abruptness 

 of the passage between the more typical An. Errantes, and the 

 Annelides of the orders TerricoLjE and TunicoLiE. 



It is probably from this discrepancy among them that, up to this 

 time, no naturalist has seized upon the characters which seem to us 

 to unite them in one, but every one has scattered its members among 

 different groups. Several of them have been considered as related 

 to the Earth-worms, others to the Nereides, and a certain number 

 have been collected together by M. de Blainville in his family 

 " Nereiscoles." The end which that zoologist had in view in the 

 establishment of that family is very nearly the same which has led 

 us to unite in one distinct group the Annelides in question ; and it 

 is probable that if Blainville had personally observed a greater num- 

 ber of species, his opinions relative to the composition of the family 

 would have been more in unison with ours than they happen to 

 be.* 



The ARiciADiE have in general the elongated linear form of the 

 Nereides and Euniciadee, but their body is not truncated in front 

 as in these Annelides, rather diminishing, on the contrary, in thick- 

 ness at the cephalic extremity. It is nearly cylindrical, and is com- 

 posed of a very considerable number of narrow segments. The head 

 is small, — often not to be distinguished from the superior lip, and 

 it is not distinctly separated from the body. The antennae are in 

 general obsolete, but in some of the genera more than usually de- 

 veloped ; while the eyes are either wanting or very minute. The 

 proboscis is very short., and does not perceptibly exceed the cepha- 

 lic segment : it is rather membranous than fleshy, and is never fur- 

 nished with jaws* but sometimes we observe tentacula in it. The 

 anterior rings of the body are narrow, and have always ambulatory 

 feet, which, in general, are slightly prominent, and divided into two 



* A great number of the Nereiscoles of M. de Blainville are only imperfectly 

 known by the descriptions of Muller, Otho Fabricius, &c. and ought, in_the 

 opinion of Audouin and M. Edwards, to'be referred to the Euniciadee ,■ while in 

 the works of these authors the Annelides, with a few exceptions, which consti- 

 tute the present family, are not to be found, and could not take a place among 

 the Nereiscoles, if regard were to be had to Blainville's character of it- Hence 

 Audouin and M. Edwards have found a new designation necessary to prevent 

 confusion. 



