296 ANNULATA. 



Numerous tentacula encircle the mouth, and on each side of the fore part 

 of the back are pectiniform branchiae. 



Some of them construct light tubes of a regularly conical, figure, which 

 they carry about with them. Their gilded setae form two combs, whose 

 teeth incline downwards. Their capacious and frequently flexed intestine 

 is usually filled with sand. 



SYPHOSTOMA, Otto. 



On the superior part of each articulation, is inserted a fasciculus of fine setae, 

 and on the inferior a simple seta, and on the anterior extremity two fasci- 

 culi of strong golden coloured setae. Under these setaceous appendages 

 is the mouth, preceded by a sucker surrounded by numerous soft filaments, 

 which may very possibly be branchiae, and accompanied by two fleshy ten- 

 tacula. The knotted medullary cord is seen through the skin. They live 

 buried in mud. Hitherto, the genus 



DENTALIUM, Lin. 



Has always been placed in this vicinity. The shell is an elongated, arcua- 

 ted cone open at both ends, and has been compared to the tusk of an ele- 

 phant in miniature. The recent observations of M. Savigny and those of 

 M. Deshayes especially, have, however, rendered this classification ex- 

 tremely doubtful. 



ORDER II. 

 DORSIBRANCHIATA. 



The organs of the Dorsibranchiata, and the branchiae in particu- 

 lar, are equally distributed along the whole of the body, or at least 

 of its middle portion. 



At the head of the order we will place those genera in which the 

 organs are most completely developed. 



ARENICOLA, Lam. 



Branchiae, resembling small trees, on the rings of the middle part of the 

 body only; the mouth, a fleshy and more or less dilatable proboscis, and 

 neither teeth, tentacula, nor eyes visible. The posterior extremity not only 

 wants the branchiae, but the setaceous fasciculi with which the rest of the 

 body is furnished; the cirri totally deficient. 



Arcn. piscatorum, Lam. Very common in the sand on the sea shore, 

 where it is disinterred by the fishermen, who use it as bait. It is about a 



