140 A renicolidae 



describe a new species A. branchialis regarding which they gave 

 the following particulars : " Cette espece, que nous avons rencontre 

 pres de Saint-Malo, est beaucoup plus petite que la precedente, et 

 s'eii distingue principaleinent par le nombre des pieds et des branchies. 

 Ces derniers organes, au lieu de comuiencer au-dessus des pieds de 

 la septieme paire, ne se montre que sur 1'anneau qui porte les pieds 

 de la treizierne ou quatorzierne paire, et au lieu d'etre au nonibre de 

 treize paires, on en compte de dix-neuf a vingt paires. Du reste, 

 cette espece ne nous a presente rien de particulier." In the general 

 description of the genus Arcnicola the authors pointed out that this 

 worm is divisible into three regions (a) an anterior, abranchiate, 

 and generally dilated, (b) a middle branchiferous, and (c) a posterior 

 apodous. The reference letters, a, b, c, are placed alongside the 

 corresponding regions in the figures of A. piscatwum and branchialis. 

 The latter figure represents a specimen about 117 mm. long, in which 

 are indicated thirty-one pairs of notopodia, beyond the last of which 

 is a region (lettered c), about 9 mm. in length, without chaetae and 

 gills. This region, consisting of six rings, of which the terminal one 

 is the largest, is almost as long as the three preceding chaetiferous 

 segments. The first right gill is shown on the fourteenth segment, 

 the first left one on the thirteenth ; there are eighteen gills on the 

 right side of the worm and nineteen on the left. 



It is not surprising that most subsequent authors inferred, from 

 Audouin and Edwards' account, that in A. branchialis the occurrence 

 of a " tail" of some extent was to be expected. Some writers greatly 

 exaggerated the length of this region, for instance, Chenu figured a 

 specimen, labelled A. branchialis, in which are shown thirty-one 

 chaetiferous segments, the last nineteen of which are branchiferous, 

 followed by a tail as long as the branchial region. Quatrefages 

 added to the diagnosis of A. branchialis the statement " Cauda 

 quartam partem corporis circiter aequans," and wrote (p. 266) that 

 " 1'A. branchiale, dont la region caudale est presque aussi developpee 

 que dans 1'A. des pecheurs," was distinguished by this character from 

 A. ccaudata. Johnston stated that A. brajichialis and piscatoruru 

 " agree in having an abranchial tail," and remarked that there was no 

 complete specimen of the former in the British Museum collection. 

 Probably the fact that none of the specimens exhibited such a tail 

 as he expected to find induced him to regard them as incomplete. 

 His ideas of the characters of A. branchialis were not clear, for the 

 specimens which he labelled with this name include examples of 

 both the ecaudate species (see pp. 134, 135). 



