TELETHUSJE. 55 



neurilemma. A single neural canal occurs in the median line just within the neurilemma 

 in the anterior part of the body. As in other forms the nerves leave the lateral part of 

 the cords, and slope downward to the muscular layer. Posteriorly the nerve-trunks are 

 less rounded, the long diameter being vertical, but the single neural canal persists superiorly. 



Though the family was first constituted by Savigny under the title of Telethusas, yet 

 in accordance with the rules adopted in other cases the term Arenicolidae suggested by 

 Audouin and Milne Edwards is perhaps more appropriate. 



Montagu 1 (1808) figures " Arenicola ceraleata" with only seven pairs of branchiae 

 and a tail. It is probably an abnormal specimen. His Lumbrieus congesticia is also 

 an Arenicola. 



Cuvier (1817) placed the genus Arenicola at the head of the Dorsibranchs, and 

 thought that five blackish patches anteriorly represented the testicles, the eggs swimming 

 in the interior of the body. 



The Telethusse formed the second family of De Blainville's (1828) second order 

 Paromocriciens, a group containing a heterogeneous series from Amphinome to Marphysa. 



This group formed the tenth family (Arenicoliens) of Audouin and Milne Edwards 

 (1834), who thought they linked the errant to the sedentary annelids, mentioning that 

 Savigny ranged them amongst the Serpulidae, whilst Cuvier placed them with the 

 Dorsibranchs. 



Grrube (1851) adopted Savigny's title Telethusa for this family, under which he also 

 included Dasi/hranchus (his Dasijmallus) now grouped with Capitellidse. 



De Quatrefages 2 (1850) agrees with the description of the circulation given by Milne 

 Edwards, and adds that ventrally the vessels pass upward on the gut and form a series of 

 caeca having the aspect of villosities on the chloragogenous coat. 



This author 3 states that the cephalic mass in A. marina is single, and gives off only 

 a nerve on each side to the auditory organ (described by Stannius). The oesophageal 

 connectives are slender, and the only representative of a visceral nerve is a small twig 

 which leaves the connective of each side immediately after its commencement. The 

 ventral cord is single with ganglionic enlargements in each segment from which the lateral 

 trunks pass. 



The same author at a later period (1865) gives a brief historical summary pointing 

 out how the lob-worms were at first confounded with the earth-worms ; then Lamarck 

 separated them as a genus, and Savigny made the family Telethusse ; subsequently 

 Audouin and Milne Edwards called the group Arenicoliens. De Quatrefages outlines the 

 general structure of the family and notes the presence of an auditory organ (statocyst). 

 He arranges the genera according to the sequence of the branchiae, Arenicola having these 

 organs in sequence, whereas Ghorlzobranchia has them separated by non-branchial feet. 

 Ashworth has shown that considerable confusion occurred in the early diagnosis of the 

 species of Arenicola in the Museum at Paris. 



Kinberg 4 (1866) gave his Telethusea no special position, for they occur after the 



1 M.S. vol. Libr. Linn. Soc, 4to, pi. xxviii, fig. 2. 



2 Types Infr. de Fembranchement des Anneles, ' Ann. Sc. naf./ 3 e ser., t. xiv, p. 283, etc. 



3 Ibid., p. 366 (sep. copy). 



4 < Qfversigfc K. Yet. Akad. Forhandl./ p. 355. 



