DORSIBRANCHIATjE. 
133 
The shell of some of them is angular * * * § , or longitudinally striated f. 
That of others is round 
c 
ORDER II. 
DORSIBRANCHIAT^. 
The organs of the Dorsibranchiatm, and the branchiae in parti- 
cular, are equally distributed along the Avhole 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 pro- 
boscis; and have neither teeth, tentacula nor eyes, visible. The posterior 
extremity not only wants the branchia?, but the . setaceous fasciculi 
Avith Avhich the rest of the body is furnished ; the cirri totally de- 
ficient. 
Aren. piscatorum, Lam.; Lwmhricus marinm, L. ; Pall. Nov. 
Act. Petrop.,ii, 1 , 19 — 29 . Very common in the sand on the 
sea-shore, Avhere it is disinterred by the fishermen, Avho use it as 
bait. It is about a foot long, of a reddish colour, and diffuses 
an abundant yelloAvish liquid Avhen touched. It has thirteen 
pairs of branchise 1|. 
Ampiiino.aie, 
A pair of more or less complex, tufted or plumose branchise on each 
ring of the body, and. to each of the feet tAVO fasciculi of separate 
setae, and tAvo cirri ; no jaAVS to the proboscis. The Amphinomes 
are divided by M. Savigny into 
* Dent, elephanfiitm, Martini, I, 1, 5, A; — Dent, aprinum, Ib., 4, A; — D. stria- 
fuhun, Ib., 5, B ; — D. arcuatum, Gualt., X, G ; — D. sexangutum. 
-f- Dent, dentatis, Rurapf., Mns., xli, 6; — D. fasciulum, Martini, Conch., I, 1, 3, 
B; — D. rectum, Gualt., X, H, &c. 
X Dent, entalis, Martini, I, i, 2, &c. 
§ M. Savigny has made a family of this genus by the name of Thelethus.e, 
which has been adopted by his successors. 
II Add, Arcnicola clavafa, Ranzani, dec. I, p. G, pi. i, f. 1, should it prove to be a 
distinct species. 
This genus has very properly been withdrawn by Brugic'res, from the Aphrodit.e 
of Pallas and the Terebell.e of Gmelin. It forms the type of M, Savigny’s 
family of the Ampiiixom.e, also adopted by his successors. 
