ORDER DORSIBRANCHIA. 17 



aprinum, ib. 4. A. ; D. striatulum, ib. 5. B. ; D. arcuatum, 

 Gualt. X. G. ; D. sexangulum. Dent, dentalis, Eumph. Mus. 

 xli, 6 ; D. Fasciatum Martini, Conch, i. 1. 3. B. ; D. rectum, 

 GuEilt. X. H., &c. 



Others have round shells: Dent, entalis, Martini, I., i. 1, 2, 

 &c. 



SECOND ORDER OF ANNELIDA. 



THE DORSIBRANCHIA, 

 Have their organs, especially their gills, distributed pretty 

 equally along their whole body, or at least along its middle 

 portion. 



We shall place at the head of the order, the genera whose 

 gills are the most developed. 



Arenicola, Lam., 



Have gills in the form of arbuscula, on the rings of the 

 middle part of their body only ; their mouth is a fleshy 

 proboscis, more or less dilatable, and neither teeth nor tenta- 

 cula, nor eyes are visible. The posterior extremity is not 

 only destitute of gills, but also of the parcels of silky hairs, 

 which furnish the rest of the body. No cirrhus exists to any 

 ring of the body. 



M. Savigny has made of this genus, a family which he names 

 Thelethusa, and which has been adopted by his successors. 



The known species, Aren. piscatorum, Lam., Lumbricus 

 marinus,lj. Pall. Nov. Act. Petrap. II. i., is very common on 

 the sand on the sea-shore, where the fishermen go in search 

 of it with spades, to use it as a bait. It is about a foot long, 

 of a reddish colour, and diffuses, when it is touched, an 

 abundant yellowish fluid. It has thirteen pairs of gills. Add. 



VOL. XIII. C 



