454 ANNELIDES. 



the operculum recall to our minds the foot of the Vermeti and Sili- 

 quariae, which have been placed among the Mollusca, the branchiae 

 strongly remind u"s of those of the Amphitriies and Tcrebellae. 

 Ulterior observations upon their anatomy, and principally upon that 

 of their nervous and vascular system, will resolve this problem. 



The shell of some of them is angular(l), or longitudinally stri- 

 ated(2). 



That of others is round(3). 



ORDER II. 

 DORSIBRANCHIATiE. 



The organs of the Dorsibranchiatae, and tlie branchiae in 

 particular, 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. (4) 



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

 of the body only; the mouth, a fleshy and more or less dilatable pro- 

 boscis, and neither teeth, tentacula nor eyes visible. The posterior 

 extremity not only wants the branchicC, but the setaceous fasciculi 

 Avith which the rest of the body is furnished; the cirri totally defi- 

 cient. 



Jlren. piscatorum, ham.; Liimbricus marinus, L-; Pall. Nov. 

 Act. Petrop. , ii, 1, 19 — 29. 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 foot long, of a reddish colour, and diffuses 



(1) Dent, elephantium, 'Martini, I, 1, 5, A; — Deiit. aprinum, lb., 4, A; — D.stria- 

 tulum, lb., 5, B; — D. arcuatum, Gualt., X, G; — D. sexangulum. 



(2) Dent, dentalis, Rumpf., ^lus., xli, 6; — D. fasciatum. Martini, Conch., I, 1, 3, 

 B;— Z). rectum, Gualt., X, H, &c. 



(3) Dent, entalis. Martini, I, i, 1, 2, &c. 



(4) M. Savigny has made a family of this genus by the name of Thelethus;e, 

 which has been adopted by his successors. 



