GENUS CO LAC I UM. 



395 



Colacium calvum, Stein. Pl. XXI. Figs. 30-32. 



Sedentary zooids elliptical or oblong, about two and a half times as 

 long as broad, of even width throughout, scarcely rounded and almost 

 square at the two extremities, elevated at an even altitude upon a very 

 short, thick pedicle, the main stem and subsequent subdivisions of which do 

 not equal a total height of one-half that of a single zooid ; motile zooids 

 highly contractile and variable in form, usually widest anteriorly; endo- 

 plasm, with the exception of a clear, cap-like, longitudinally striate, anterior 

 area, enclosing numerous, minute, spherical chlorophyll-corpuscles, each 

 with a central nucleus-like point ; contractile vesicle large, communicating 

 freely with the tubular pharynx ; endoplast conspicuous, situated in the 

 median line at a distance of one-third of the length of the body from the 

 posterior extremity. Length of sedentary zooids 1-500". 



Hab. — Fresh water, mostly forming small colonies of two or four 

 zooids only. 



Colacium vesiculosum, Ehr. Pl. XXI. Figs. 34-38. 



Sedentary zooids subfusiform, about two and a half times as long as 

 broad, tapering towards each extremity, but more attenuate posteriorly 

 when extended, pyriform and widest anteriorly when contracted, seated at 

 the same level at the summit of a short, slender, and often transversely 

 wrinkled, branching pedicle, the entire height of which scarcely equals one- 

 half of that of an extended zooid ; motile zooids Euglena-like, variable in 

 form. Chlorophyll-corpuscles of endoplasm oval, numerous and equally 

 distributed. Length of sedentary zooids 1-800". 



Hab. — Fresh water, on Cyclops and other Copepodous Crustacea ; colony- 

 stocks including from two to eight animalcules. 



Colacmm Steinii, S. K. Pl. XXI. Figs. 39-41. 



Sedentary zooids elongate-ovate, about two and a half times as long as 

 broad when extended, globose, pyriform, or subnapiform, with an inflated 

 central and conically projecting anterior and posterior prolongation when 

 contracted ; pedicle branching irregularly or subdichotomously, bearing the 

 zooids at different heights and attaining an altitude equal to two or three 

 times that of an extended animalcule ; motile zooids Euglena-like, variable 

 in form ; endoplasm enclosing numerous, evenly distributed, ovate chloro- 

 phyll-corpuscles. Length of sedentary zooids 1-900". 



Hab. — Fresh water, on a species of Cyclops. 



In the general contour of the extended zooids and comparative altitude of the 

 supporting pedicle, this species corresponds considerably with C. arbiisculum. It 

 may be distinguished from it, however, by the more or less irregular instead of even 

 dichotomous divarication of the secondary branches and by the elevation of the 

 animalcules at diverse instead of corresponding heights. During their contracted 

 state the napiform contour referred to in the diagnosis is of common occurrence, 

 but does not, from Stein's figures, appear to be assumed by either of the preceding 

 types. While this last-named contour is the most characteristic, innumerable other 



