118 CILETOPTERID^. 



is small in the thorax, yet large membranous sacs occur on the anterior wall of the 

 dissepiments (Claparede). 



The nerve-cords are separated in front and are within the circular coat, but they 

 unite in the middle region, whereas they remain separate in Telepsavus. The cerebral 

 ganglia are much diminished, the eyes in both forms being placed on the surface of the 

 transverse commissure. 



The segmental organs in the abdomen of Ohsetopterus are conspicuous coiled structures, 

 the upper part of which differs from the lower, having polyhedral cells, with rounded 

 concretions which give a chalky aspect. They lie externally above the great ventral 

 muscle — between it and the ovary. The cavity of the tube is filled with concretions. 



Renier l gave the name of Tricodia variopedata to this species in 1804 in his ' Prosp. 

 della Classe dei Verm.,' p. 18, and later (1847) a posthumous volume was published, con- 

 taining a good description with excellent coloured figures both of the animal and its tube. 

 The bristles, however, are on too small a scale for accurate details. In one of the figures 

 (Fig. 6) a pair of peculiar flattened and serrated long lamella project from the anterior 

 end as if a longitudinal slit had been made in the first region. The name Ohsetopterus 

 was given by Cuvier in 1830, and has been generally adopted by zoologists. 



Busch 2 (1851) describes and figures a larval form from Trieste which most nearly 

 approaches Spiochsetopterus. The structure of its body and bristles is typical. 



R. Leuckart placed this anangian family (as he thought) near the Ariciidas, but Sars 

 considered it was more closely allied to the Spionidse, especially, as Claparede shows, after 

 the study of Spiochsetopterus, Phyllo ohsetopterus, and Telepsavus. The latter author (1868) 

 draws attention to the occurrence of the special bristles in Polydora, Disoma, and Chsetop- 

 terus. Notwithstanding Renier's circumstantial account of the vascular system of 

 Ghsetopterus variopedatus, the anangian condition was maintained by various authors. 



The free swimming larva of Chastopterus (?) was first described by J. Miiller 3 under 

 the name of Mesotrocha; again by Busch 4 and by Max Muller, 5 whose figures, however, 

 show remarkable hooks which differ from anything known in the group. Such figures as 

 Claparede and Mecznikow give of other members of the family indicate that further 

 investigation is necessary in Chastopterus variopedatus. 



Grube (1865) adopted the family Chastopterea after Audouin and Edwards, placing 

 it between the Chloraemida) and Arenicolidse. He entered two species, 0. norwegicus and 

 G. pergamentaceus, but they probably refer to the same form. 



The Cha3topterida3 formed the first family of De Quatref age's Sedentary Annelids 

 (1865), which were characterised by having the body divided into regions. He disagrees 

 with Cuvier's location of the group at the end of the Dorsibranchs and near the Poly- 

 noidse. Audouin and M. Edwards, again, raised them to the rank of a family immediately 

 in front of the Arenicolidae ; whilst Grube included them under his Limivora (agreeing 



1 < Osservazioni postume de Zool. Adriatica del Professore Stefano Andrea Renier/ published 

 under the care of Prof. G. Meueghini, Venezia, 1847. 



2 ' Beobach. Anat. u. Entwickel. Wirt). Seeth./ p. 59, Taf. ix, figs. 1—8. 



3 f Archiv Anat. u. Physiol., 1846/ p. 104. 



4 Op. cit., p. 58. 



5 ' Observat. Anat. Verm. Maritim./ p. 25, Tab. iii, figs. 14—17. 



