GENUS RHIPIDODENDRON. 285 



divaricating at an approximately uniform angle of 45, while in the second and 

 larger specimen these, while branching in the same plane, curve about in an alto- 

 gether irregular manner. It is possible that this less regularly constructed tenement 

 represents an instance in which the food supply had been less plentiful, the tubular 

 fabric excreted losing through such a cause as in the branching stalk Q{ Anthophysa 

 vegetans its characteristic more erect and rigid bearing. In this comparatively 

 irregular example, there would also appear to be an entire absence of the dissepi- 

 ments or joint-like structure developed at each point of bifurcation in the more 

 symmetrical and rigid form. The adult colonies of this species, according to Stein's 

 figures, contain from but ten to fourteen zooids ; the tubules, immediately succeeding 

 the act of longitudinal fission of the enclosed zooids and preceding the further 

 development and bifurcation of the ramuscule, necessarily enclose two animalcules. 



GENUS II. RHIPIDODENDRON, Stein. 



Animalcules ovate, with two anteriorly inserted, attenuate and equal- 

 sized vibratile flagella, living in social colonies, and building up a flabellate 

 or dendriform aggregation or zoothecium of closely approximated granular 

 tubules, the cavities of which are separately inhabited by a single zooid ; 

 contractile vesicle and endoplast conspicuous ; no distinct oral aperture. 

 Inhabiting fresh water. 



Rhipidodendron splendidum, Stein. PL. XVI. FIGS. 1-3. 



Aggregated tubules of the colony-stock forming an erect, compressed, 

 flabelliform, profusely branching zoothecium ; animalcules evenly ovate or 

 elliptical, usually occupying the distal extremity of these tubules, their 

 flagella only projecting into the surrounding water ; flagella of equal size, 

 about twice the length of the body ; contractile vesicle and endoplast 

 situated close to each other a little behind the centre of the body ; paren- 

 chyma transparent, granular. Length of zooids 1-2000", height of adult 

 zoothecium 1-75". HAB. Fresh water. 



The plate devoted by Professor Stein to the illustration of this most remarkable 

 type* may be justly described as forming the gem of the entire series contained in 

 his recently issued and important work. The innumerable members of the extensive 

 colony-stock build up an aggregated structure that may be compared most appro- 

 priately with the similarly fan-shaped, tubular polyparies of the Cyclostomatous Poly- 

 zoon Tubulipora flabellaris. As suggested by Stein, it would seem just possible that 

 the Aporca ambigua, described by J. W. Bailey in vol. ii. of the ' Smithsonian Con- 

 tributions ' for 1850 as a doubtful algoid or stalked infusorial product, is identical 

 with this type ; this earlier name, in the event of such identity being substan- 

 tiated, will necessarily take precedence of Stein's. So far as it is possible to decide 

 in the absence of full descriptive details, the ramifying tubular zoothecium of this 

 interesting species would seem to be homologous with the solid branching pedicle or 

 zoodendrium of Anthophysa vegetans, its tubular instead of solid character resulting 

 through its secretion or excretion from the entire periphery of the individual animal- 

 cules, instead of from their posterior extremity only. As delineated by Stein, the 

 consistence of this excreted zoothecium exhibits a distinct granular aspect, and is, 

 in accordance with the accompanying explanation, of a rust-brown hue. In the 

 larger example figured by this authority, and here reproduced, PI. XVI. Fig. i, 



* 'Infusionsthiere,' Abth. iii. Taf. iv., 1878. 



