ZOOLOGICAL AND BOTANICAL ASSOCIATION. 117 



vatum aro often very obscure. The separated joints of the form of 

 which I havo tried to convey a conception, considerably resemble a 

 minute form of Cosmarium, and such I thought a single joint was till 

 I met it in lengthened filaments. To obviate the difficulty here met 

 with, two courses may appear to be open : either to allow this plant to 

 remain as an aberrant member of the genus Spheerozosma — an unadvi- 

 sable course if it could be avoided— or else to alter the characters of the 

 genus by omitting the " junction-glands" as essential to it, for it appears, 

 I think, that the plane or compressed filament is itself enough to distin- 

 guish Sphaerozosma from the cylindrical or angular filamentous genera, 

 ix( ept, perhaps, Aptogonum desmidium, fi, which, however, is distin- 

 guished by the foramina between the joints. This view I would, then, 

 very submissively put forward. In any case I do not see I have an alter- 

 native but to describe this form as a Sphaerozosma, as follows : — 



Sphzrowsma pulchellum (nov. sp.). 



Filament very minute and fragile; joints (including inflations) about 

 as broad as long ; ends truncate, with square angles ; segments suddenly 

 inflated at the base, and separated from each other by a shallow acute 

 notch, thus giving to the margin, at each side, a pouting appearance at 

 the central constriction, each segment of the joints containing a single 

 central light-coloured corpuscle. 



Length of joint, ^sVs in.; diameter of joint at the end, ttjStjJ diameter 

 at widest part of inflation, Wto in. 



I have also to bring to notice a species of Staurastrum, which, though 

 minute, and not very striking in appearance, there can be no doubt is 

 an undescribed one. In the front view this little organism might pos- 

 sibly be taken for a small form of Arthrodesmus incus (Figs. 8, 10); but 

 the central constriction is not so deep, nor is the constricted portion so 

 narrow, nor are the segments comparatively so dilated at the ends, nor is 

 the gibbous appearance at the base of the segments often seen in Arthro- 

 desmus incus present in the form in question ; however, an end view, 

 showing its four, or frequently three angles, dispels all doubt, and at 

 onoe proclaims the plant a Staurastrum (Figs. 9, 11). It differs from 

 Staurastrum defectum (Brtb.) by its much smaller size and less deep con- 

 striction, and angles not inflated in the end view; from Staurastrum 

 cuspidatum (Brib.), the end view of which the triangular variety most 

 approaches, by its much smaller size, straight sides in end view, and non- 



