282 ARTICULATA. 



medullary cord is seen through the skin. They live buried in mud. Hitherto, 

 the genus 



DENTALIUM, Linnaus, 



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

 cone open at both ends, and has been compared to the tusk of an elephant in 

 miniature. The recent observations of M. Savigny, and those of M. Deshayes 

 especially, have, however, rendered this classification extremely doubtful. 



ORDER II. 

 DORSIBRANCHIATA. 



THE organs of the Dorsibranchiata, and the 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, Lamarck. 



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. 



Aren. 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 foot long, 

 of a reddish colour, and diffuses an abundant yellowish liquid when touched. 

 It has thirteen pairs of branchiae. 



AMPHINOME, Bruguieres. 



A pair of more or less complex, tufted or plumose branchiae on each ring of 

 the body, and to each of the feet two fasciculi of separate setae, and 

 two cirri; no jaws to the proboscis. The Amphinomes are divided 

 by M. Savigny into CHLOKIA, in which the head is furnished with 

 five tentacula, the branchiae resembling a tripinnate leaf. Of these 

 the Indian ocean produces one very remarkable for its long bundles 

 of lemon-coloured setaa, and the beautiful purple plumes of its 

 branchiae. Into PLEIONE, where with the same tentacula the bran- 

 chiae are tufted, also from the Indian ocean; some of them very 

 large '; EUPHROSINE, where the head has but a single tentaculum, and 

 the tree-like branchiae complex and much developed; and into 

 HIPPON*, which has no caruncle, and but a single bundle of sits?, 

 and a single cirrus to each foot. 



