GENUS NASSULA. 



495 



even, straight, undilated tube ; contractile vesicle single, spherical, sub- 

 central ; numerous vesicular spaces, with violet-coloured contents, usually 

 present in the anterior region ; no trichocysts. Length of body 1-96". 

 Hab. — Pond water. 



The Nassula elegans and N. conica of Ehrenberg appear to differ from this species 

 merely in the subordinate character of colour, the former variety being white or 

 greenish and the latter yellow or brown. 



Nassula flava, C. & L. 



Body elongate, cylindrical, three or four times as long as broad, slightly 

 depressed in the antero-dorsal region ; colour mostly yellow or brick-red ; 

 pharyngeal armature consisting of numerous rod-like teeth, the tube they 

 form being much dilated at the distal end ; anterior extremity of the 

 cortical layer usually containing numerous violet-coloured corpuscles, which 

 do not circulate with the general contents ; contractile vesicles two in 

 number, simply spherical. Length of body 1-240" to 1-125". 



Hab. — Pond water, among Oscillator ia. 



This species, while differing from N. orjiata Ehr,, as explained by Claparede and 

 Lachmann, in the form of the pharyngeal tube and the possession of two contractile 

 vesicles, approaches it so closely in all other details as to render it doubtful 

 whether it must not be regarded as a mere local variety of that type. 



Nassula ambigua, Stein. Pl. XXVI. Fig. 41. 



Body shortly oval or elliptical, cylindrical, equally rounded at both 

 extremities, not quite twice as long as broad ; pharyngeal armature con- 

 sisting of a simple horny tube dilated at its anterior extremity ; contractile 

 vesicle single, spherical or assuming a stellate outline, medianly located. 

 Length of body 1-240". Hab. — Pond water. 



A species, apparently identical with this form, recently obtained by the author 

 from ditch water at St. Heliers, Jersey, exhibited numerous trichocysts in the 

 substance of its cortical layer, and was coloured deep green, more especially in the 

 posterior region, through the inception of food-particles. While the first example 

 observed showed apparently a simply tubular pharynx, other specimens, examined 

 with a higher magnification, revealed the presence of the rod-like teeth characteristic 

 of the two preceding forms. 



Nassula rubens, C. & L. 



Body elongate, cylindrical, three times as long as broad, equally rounded 

 at the two extremities, brick-red or rose colour ; pharyngeal armature con- 

 sisting of separate rod-like teeth, the tube formed by them being slightly 

 dilated anteriorly ; trichocysts large and abundant ; contractile vesicle 

 single, spherical, subcentral. Length 1-500". Hab. — Pond water. 



This species is identified by Claparede and Lachmann with the Cydogramma 

 ruhens of Perty. The genus Cyclogmmma, as instituted by the last-named author, 

 was distinguished from Nassula by the presence of concentric strite in or upon the 

 cuticular substance. These apparent striae are now shown to represent the im- 

 perfect optical aspect of the closely approximated trichocysts, as seen with an 

 insufiftcient defining power, that occur so abundantly in this and other species of the 



