GENUS OPERCULARIA. 713 



closely approximated and appear to be attached in a sub-sessile manner. 

 Length of extended zooids 1-200". 



HAB. Fresh water, on the crustacean Asellus aquaticus. 



In the absence of any figure of this species given by Stein, the illustration of 

 the same form accompanying D'Udekem's account of the animalcule as obtained 

 by him on Asellus aquaticus in the neighbourhood of Brussels, is herewith reproduced. 

 It is at the same time desirable to remark that while in D'Udekem's examples as 

 here figured the length of the extended zooids agrees with that given in the above 

 diagnosis, Stein attributes to them one of the 1-900" only, and that of 1-360" to 

 the entire colony-stock. 



Opercularia microstoma, Stein. PL. XXXIX. FIG. 16. 



Bodies irregularly pyriform, constricted behind the middle line, and 

 thence tapering towards the posterior extremity, about one and a half 

 times as long as broad; peristome and ciliary disc exceedingly narrow, 

 the last-named structure but slightly elevated ; membranous collar obliquely 

 set, presenting a tongue-like aspect ; endoplast curved, hamate ; pedicle 

 very short, its entire height not equalling that of a single extended zooid, 

 the ramifications comparatively slender, usually marked by thickly set 

 annular constrictions, which render it more or less crooked or knotty, 

 but sometimes entirely smooth. Greatest length of bodies 1-280". 



HAB. Fresh water, attached to the limbs of various Entomostraca ; 

 colonies including but few animalcules. 



Stein remarks that this species, in both the form of the zooids and in the growth 

 and proportionate size of the pedicle, presents a strong resemblance to Opercularia 

 stenostoma, from which, however, it may be distinguished by its larger size, thicker 

 proportions, and more conspicuously developed hyaline collar. While the colonies 

 more usually include two or four zooids only, instances are cited in which about 

 twenty were observed grouped upon a single pedicle ; this last-named structure, not- 

 withstanding its branched condition, did not exceed the relative height quoted in 

 the foregoing diagnosis. The author has recently, January 1878, obtained small 

 colonies of this animalcule in company with Cothurnia astaci attached to the Ento- 

 mostracon Canthocamptus minutus taken from a roadside pond near Acton. The 

 pedicle in all the examples examined was completely smooth, while the cuticular 

 surface, under a magnification of eight hundred diameters, was shown to be finely 

 striate transversely. 



Opercularia cylindrata, Wrz. PL. XXXIX. FIG. 21. 



Bodies elongate, cylindrical, slightly tapering posteriorly, truncate 

 anteriorly, about two and a half times as long as broad ; peristome-border 

 scarcely differentiated, not dilated : ciliary disc very slightly elevated ; 

 vestibular cleft spacious, produced backward to a distance of one-third of 

 the length of the body ; cuticular surface finely and closely striate trans- 

 versely; endoplast elongate, band-like, longitudinally disposed; pedicle 

 tall, with subequally long, slightly curved, secondary branches, closely 

 striate transversely throughout its entire length, its main stem coloured 

 brown, colonies including numerous individuals. Length of bodies 1-500". 



HAB. Fresh water, on Cyclops quadricornis. 



