844 MR JAMES RITCHIE ON 



that in the Hull colonies specimens are to be found with sometimes the dumpy uniform 

 internodes of an " Arthropodaria," and at other times the lengthy attenuated internodes 

 of a " Gonypodaria," must be taken to show that the generic distinction drawn by 

 Ehlers cannot be a valid one. Indeed, the genus Arthropodaria as defined by Ehlers 

 does not exist, so far as is known, but falls within the genus Gonypodaria of the same 

 author, which is included in Barentsia. Arthropodaria benedeni then becomes Barentsia 

 benedeni (Foettinger). 



I agree with Foettinger as to the apartness of Barentsia gracilis and B. 

 benedeni. The most apparent distinction between them lies in the stem, which in the 

 latter is normally jointed, being formed of up to eight regular, uniform internodes in 

 which an approximately constant proportion exists between the sizes of the muscular 

 and non-muscular portions. Since the former exceed the latter in length, the stem has 

 a great power of movement. In B. gracilis, on the other hand, the simple stem, 

 with only a basal muscular swelling ("musculium" of Jullien and Calvet) is the 

 normal individual, while in jointed examples the internodes never exceed four in 

 number, and are very irregular in size and shape, no definite relationship existing 

 between the sizes of the muscular and non-muscular portions, except that the latter 

 always exceed the former in length. Through the exaggeration of the rigid portions, 

 the mobility of the stems of B. gracilis is obviously greatly reduced. A difference 

 in robustness also exists, for the cuticle of the rigid portion is much more strongly 

 developed in B. benedeni, as also is that of the nodal septum, which in B. gracilis 

 forms only a very insignificant annular ridge within the stem. In B. benedeni there 

 arise from the internodes buds which develop into accessory stems ; such internodal 

 budding appears not to occur in B. gracilis. 



Foettinger and Loppens # also lay stress upon the distinction that in B. belgica 

 a " collerette " surrounds the tentacles, but that in B. benedeni no such structure 

 exists. I am of opinion that this distinction is non-existent. The structure which 

 occurs in B. belgica, as in the Hull specimens, is not a "collerette" in the sense of 

 being anything different from the free margin of the calyx. It consists of a thin 

 transparent membrane which is bordered by the atrial sphincter band of muscles, and 

 from the margin of which the tentacles arise. This membrane, however, does not 

 surround the tentacles as a separate sheath, as van Beneden states (op. cit., p. 24), 

 nor are the tentacles situated along its inner surface ; for they arise from its margin, 

 although rows of flattened cells continue the line of the tentacles on the delicate 

 wall of the calyx, and might suggest that the tentacles as distinct cylindrical bodies 

 were continued there (see PI. I. fig. 2). 



Van Beneden's description and figures prove that this so-called "collerette" exists 

 in his Pedicellina belgica ; my own observations show it to be present in the Hull 

 specimens, and although my specimens of B. benedeni are contracted, 1 am convinced, 



* K. Loppens, " Bryozoaires marins et fluviatiles de la Belgique," Ann. Soc. Roy. Zool. Malac. Belgique, 

 vol. xli., 1900(1907), p. 300. 



