DORSIBRANCHIATA. 393 



terminates behind into a tube recurved over the head, doubtless for tlie purpose of emitting their excrements. 1 

 have found in them a muscular gizzard. 



Such upon our coasts is the Sabella alveolaia, Gnielin, or Tubiporaarcnosa, Linn., the tubes of which, united 

 into a compact mass, present orifices rather regularly disposed, like the cells of a honey-comb. The Amphitrite 

 pliimosa, Fabr., should perhaps range here, of which M. Blainville has formed his genus Pherusa. Amph. ostrearia, 

 Cuv., establishes its tubes upon Oyster-shells, and is reputed to check the propagation of their inmates. 



To this order I suppose must be approximated 



The Svphostoma, Otto, — 

 Which have a bundle of fine silky bristles above each articulation, a simple bristle below it, and at the 

 fore extremity two bundles of stiff and gilded bristles, beneath which is the mouth, preceded by a 

 sucker encircled by many soft filaments, that perhaps subserve the office of bianchise, and which are 

 accompanied by two fleshy tentacles. Their medullary nervous cord may be seen through the skin of 

 the belly. They live deep in the mud. 



The species are S. diplochoites, Otto, and S. uncinata, Aud. and Edw. 



Lastly, in the vicinity of the same group, has lately been placed 



Dentalium, Linn., — 

 The species of which have a shell in form of an elongated cone, arcuated, and open at both ends, 

 which maybe compared to an Elephant's tusk in miniature ; but the recent observations of M. Savigny, 

 and especially of M. Deshayes, render this classification very doubtful. 



The animal does not appear to have any appreciable articulations, nor 

 lateral silky bristles ; but it has a membranous tube, in the interior of 

 which is a sort of foot, or fleshy and conical operculum, by which it closes 

 the orifice. At the base of this foot is a small, flat head, and there are 

 feather-like branchias upon the neck. If the operculum approximates the 



F.g 202.— Dentalium entalis, in its ' t ii' 



'"i^p- foot of the Tubulibranchiate Mollusks {Vftrmetus and Siliquaria), the gills 



are rather those of Amphitrite and Terelella. Further observations on their anatomy, and principally 

 on their vascular and nervous systems, are required to solve this problem. 



Difl'erent species have the shell angular, longitudinally striated, or round. Among the first are D. elaphantinum, 

 Martini,' &c. ; among the second, D. dentalis, Rumpf. ; and among the third, D. entalis, Martini. 



THE SECOND ORDER OF ANNELIDES,— 



THE DORSIBRANCHIATA,- 



Have their organs, and particularly their gills, distributed about equally throughout the 

 length of the body, or at least its middle portion. 



AVe place at the head of them certain genera, in which the gills are more aeveloped. 



Arenicola, Lam. 



Gills of an arbuscular form, upon the rings of the middle part of the body only. The mouth a fleshy 

 trunk, more or less dilatable, but no discernible teeth, tentacles, or eyes. The posterior extremity of 

 the body devoid not only of gills, but also of bundles of silky bristles, which occur on the other part ; 

 no cirrhus on any ring of the body. ^L Savigny forms of them his family Thelethnces. 



Tne common species (Liniibriais marinits, Linn.), is very abundant in the sand of the sea shore, where the 

 fishermen dig for it to serve as bait. It is nearly a foot long, of a reildish colour, and diffuses, on being touched, 

 a fiu.uitity of yellow fluid. It has three pairs of gills. 



Am£'iiinome, Brug. 



A pair of branchiae in form of a crest, or a tuft more or less complicated, on each ring of the hodv, 

 and two bundles of separate bristles, together with two cirrhi, upon each foot. Tiie trunk or proboscis 

 witliout jaws. These form the family of Amphinomes of M. Savigny, who divides them into 



Chlocia, wherein are five tentacles to the head and gills in form of a tripinnate leaf. There is one in the East 

 \\\A\e%(TerebeUa_flava,Gm.), extremely remarkable for its long citron-coloured bundle of bristles, and for its 

 splendid purple tufts of branchia-. Its form is broad and depressed, and it has a vertical crest on the muzzle. 



