ON A NEW HISTRI013DELL1D. 301 



median, and each consists of two distinct segments, the basal 

 much shorter than the distaL They are attached a little 

 below and behind the antero-lateral border of the head at 

 some little distance from the middle line. The second pair 

 [t^] are nearly twice as long as the first, attached on the 

 antero-lateral margin of the head a little behind the first 

 pair; each consists of two segments, of which the basal is 

 somewhat longer and thicker than the distal. All the 

 tentacles are tipped with very fine non-motile sensory cilia, 

 arranged in a circlet or spiral. The remaining pair of ap- 

 pendages of the head, the anterior legs {I. a.), are of a yery 

 different character. They are much thicker than the tentacles, 

 unjointed, and retractile, being capable of becoming com- 

 pletely withdrawn into the interior of the head by the action 

 of retractor muscles. They are situated on the ventral surface 

 of the head, considerably behind the posterior tentacles. 

 They are somewhat shorter than the latter, of subcylindrical 

 form, broadest at the base, ordinarily directed outwards, 

 forwards, and downwards. At the free end is a slight expan- 

 sion, apparently of the nature of a sucker. Close to the base 

 of each is a rounded mass of unicellular glands, about half a 

 dozen in number, the ducts of which traverse the appendage 

 to its extremity. 



The body is regularly constricted at intervals, and may 

 best be described as imperfectly divided into six segments. 

 The nature of these can only be discussed after the internal 

 organs have been dealt with. All the constrictions are much 

 more strongly marked laterally than dorsally or vent rally. 

 They are clearly marked in the living specimens. The first 

 or neck segment is small, and is devoid of appendages. The 

 second has on each side a mammiform elevation, on the 

 summit of which is insei'ted one of the cirri of the first pair 

 (c^). These are slender cylindrical appendages, similar in 

 character to the tentacles, and each consisting of two segments, 

 a thicker proximal and a thinner distal. Like the tentacles, 

 the cirri are tipped with fine non-motile sensory cilia. 

 Behind tliis are three rings, which are probably to be referred 



