GENUS OPERCULARIA. 71 1 



transversely. Length of bodies 1-430" ; height of the entire polypidom, 

 1-24" to 1-9". 



HAB. Fresh water, on aquatic plants and animals ; colonies including 

 a large number of zooids, which assume a nodding or pendent position 

 with relation to their stalks at the time of contraction. 



This species is described by Ehrenberg under the title of Epistylis nutans, being 

 rightly referred to its present position by Stein. Its large, handsome, symmetrical 

 tree-like colonies attain an altitude and luxuriance of growth unequalled by any 

 other representative of the genus, and among which it is more eminently distinguished 

 on account of the singular and sudden nodding action displayed by the zooids 

 when disturbed, in place of the more ordinary phenomena of contraction. In a less 

 conspicuous degree a like property is possessed by Opercularia berberina. As with 

 the last-named species, the cuticular surface of the animalcules is considerably 

 indurated, in proof of which it may be mentioned that the author has on several 

 occasions seen the isolated cuticular investments left as empty vase-shaped trans- 

 parent sheaths after their detachment from the pedicle, and the complete dissolution 

 of the previously enclosed protoplasm. Among the figures of this species given 

 by Ehrenberg (PL XXXIX. Fig. 23) he delineates one animalcule having attached 

 to its side what he interprets to be a lateral bud, but which more probably represents 

 the conjugation of a migrant zooid with an ordinary sedentary unit. 



Opercularia articulata, Ehr. PL. XXXIX. FIGS. 24-26. 



Bodies elongate-ovate, or fusiform, truncate at each extremity; peri- 

 stome-border not thickened, but forming a simple terminal edge, with 

 often a few longitudinal plications ; remaining cuticular surface smooth 

 and soft, parenchyma usually densely granular posteriorly; ciliary disc 

 greatly elevated, bearing three circlets of cilia, membranous collar con- 

 spicuous ; endoplast horseshoe-shaped, transversely placed ; pedicle variously 

 but usually profusely and dichotomously branched, often delicately striate 

 in a longitudinal direction, exhibiting at remote distances more or less 

 distinct transverse articulations. Length of extended zooids 1-324" to 

 1-96", average 1-192"; altitude of tree-like colony 1-72" to 1-48." 



HAB. Fresh water, on Dytiscus marginalis and other aquatic Coleop- 

 tera. 



The very remarkable diversity exhibited in the sizes of the zooids of this species 

 might be expected to pertain to stocks collected from widely separated localities. 

 According to Stein, however, they may be met with in separate colonies upon the 

 same Coleopterous hosts. An almost equal amount of variation would appear 

 to obtain in the build and comparative lengths of the ramifications of the pedicle ; 

 in some neither the main shaft nor the associated branches equal more than one- 

 half of the length of an extended zooid, while in other colonies the extended 

 zooids are as proportionately small, or even smaller, with reference to their attenu- 

 ately branched supporting stem. 



Opercularia berberina, Linn. sp. PL. XXXIX. FIG. 27. 



Bodies elongate, subcylindrical, slightly contracted at the two ex- 

 tremities, two and a half times longer than broad ; peristome obsolete ; 

 ciliary disc bearing a single circlet of cilia, protrusible but a short distance 

 beyond. the margin of the peristome ; membranous collar small, not easily 



