AN ENTOPROCTAN POLYZOON (BARENTSIA BENEDENI). 847 



fine granulation. In B. gracilis, the oval masses of granules are smaller in size and 

 fewer in number, and they are confined to the basal muscular expansion of the stem. 

 The nature of the granular masses is unknown. They may be reserve stores of food- 

 material such as occur in the fresh-water polyzoon Urnatella gracilis Leidy * ; and 

 were this the case, their appearance would probably be of little specific value, indicating 

 seasonal condition rather than distinction of form. 



Perplexed by these resemblances and dissimilarities, I hesitate in attributing the 

 Hull specimens to any known species. Yet the distinctive characters are not sufficient 

 in intensity, nor is their value sufficiently ascertained, to mark the specimens as 

 belonging to a new species ; and I therefore range them with Barentsia benedeni, 

 which has hitherto been recorded only from Ostend. 



V. Summary. 



1. Specimens of a jointed-stemmed Entoproctan Polyzoon from Hull have been 

 described as belonging to Barentsia benedeni (Foettinger). The salient characters of 

 the specimens are : — Stem composed of up to 8 well-defined, robust internodes (3 or 4 

 being most common), from which buds may arise ; no pores in chitinous portions of 

 internodes ; no granular masses in internodes ; calyx relatively small, with transparent, 

 colourless walls; tentacles 10 to 14, colourless; brain trapezoid in transverse section. 



2. Consideration of the variations of this and of related species leads to the 

 conclusions that : — 



(a) Arthropodaria, Ehlers, is synonymous with Gonypodaria, Ehlers, and both are 



included in Barentsia. 



(b) Gonypodaria nodosa (Lomas) is synonymous with Barentsia gracilis. 



(c) Pedicellina belgica, van Beneden, is synonymous with Barentsia gracilis. 



(d) Barentsia benedeni (Foettinger) and B. gracilis (Sars) are distinct. 





EXPLANATION OF PLATE. 



a., 



anus. 



a.sn., 



accessory stolon budding from stalk. 



ah.n., 



abnormally placed node. 



br., 



central nerve ganglion or "brain." 



c.\ 



old calyx about to be cast off. 



c\ 



new and incompletely regenerated calyx, 



ch., 



rigid chitinous portion of internode. 



d., 



diaphragm of compressed cells. 



di., 



extraneous diatoms. 



dil., 



dilatation of internode. 



e., 



ectoderm. 



e.r., 



ectodermal ring of node-forming cells. 



9-P; 



growing point of stolon. 



* Davenport, C. B., "On Urnatella gracilis" Bull. Mus. Com}). Zool. Harvard, vol. xxiv., 1893, p. 8. 

 TRANS. ROY. SOC. EDIN., VOL. XLVII. PART IV. (NO. 27). 124 



