712 ORDER PERITRICHA. 



defined ; vestibular cleft capacious, produced backwards through one-half 

 the length of the body ; cuticular surface membranous, transversely striate ; 

 contractile vesicle located near the termination of the vestibulum ; endo- 

 plast ovate, or slightly elongate ; pedicle irregular, dichotomously branched, 

 its ramuscles curved outwards, and supporting the animalcules at various 

 heights, presenting transverse lines or joints at variable distances, no con- 

 spicuous longitudinal striae. Length of bodies 1-190", 



Hab. — Fresh water, on various aquatic insects ; zooids in the state of 

 contraction assuming a pendent posture. 



The tree-like colonies of this species exhibit as wide a range of variation in their 

 external contour as is reported of Opercidaria artiailata, but the pedicle throughout 

 all these deviations presents a similar unequal and non-corymbose formula of growth. 

 The cuticular surface is reported by Stein to be considerably indurated, and to 

 remain, as observed by the author of O. nutans^ as a transparent shell after the entire 

 disintegration of the previously enclosed parenchyma. This animalcule is synonymous 

 with the Epistylis berberifonnis of Ehrenberg and the Hydra and Vorticella berberina 

 respectively of the ' Natursystem ' and ' Systema Naturse,' ed. xii., of Linnaeus. 



Opercularia Lichtensteinii, Stein. Pl. XXXIX. Fig. 20. 



Bodies short, subcylindrical or barrel-shaped, their length not equal- 

 ling double the width, slightly narrower at each extremity, the anterior 

 one longitudinally plicate when contracted ; ciliary disc slightly elevated 

 above the peristome, bearing a single circlet of cilia ; membranous collar 

 conspicuous, notched, or crenulate ; endoplast short, oval or completely 

 round ; pedicle sparingly branched, short, exceedingly thick, not equalling 

 the height of the extended zooids, longitudinally striate, and exhibiting 

 prominent transverse rugae, dividing close to its point of attachment, the 

 ramifications increasing in width towards their juncture with the bodies 

 of the zooids, and at which point they equal or exceed one-half of the 

 diameter of these latter. Length of bodies 1-190". 



Hab. — Fresh water, on various aquatic Crustacea and Mollusca ; colony- 

 stocks including but a few animalcules. 



The short, thick, wrinkled, sparsely dividing stem of this type closely resembles 

 that of Epistylis Steifiii, but is wanting in the conspicuous central canal that 

 characterizes that species. 



Opercularia stenostoma, Stein. Pl. XXXIX. Fig. 17. 



Bodies elongate-pyriform or fusiform, widest in advance of the median 

 line, strongly contracted and almost stalk-like posteriorly ; peristome- 

 border and ciliary disc very narrow, the latter bearing a single circlet of 

 cilia ; membranous collar inconspicuous, appearing only as an annular ridge 

 above the edge of the peristome ; endoplast long, horseshoe-shaped ; 

 pedicle relatively small, rigid, dichotomously divided, bearing but from four 

 to six animalcules, striate longitudinally and obscurely wrinkled in a 

 transverse direction, the secondary branches so short that the zooids are 



