40 Mr. J. Ralfs on the British Desmidiese. 



the oral appendages. That it is a member of the Aphroditacea 

 no one can doubt, although it possesses few of the technical cha- 

 racters by which that family has been hitherto defined. It has 

 no near ally in the family. In common with the Palmyre, the 

 back is naked or destitute of scales ; but there is nothing else in 

 which the two genera agree. 



Plate II. fig. 7. Spinther oniscoides of the natural size. Fig. 8. The 

 dorsal aspect viewed through a common magnifier. Fig. 9. A view of the 

 ventral surface. Fig. 10. Two feet detached and viewed from the back. 

 Fig. 11. A foot as seen from below. Figs. 12, 13, 14. The bristles. 



[To be continued.] 



III. — On the British Desmidiese. By John Ralfs, Esq., 

 M.R.C.S., Penzance*. 



[With a Plate.] 



BiDYMOPRIUM, KiltZ, 



Filaments elongated, gelatinous, fragile, cylindrical or subcylin- 

 drical, with a bidentate process or angle on each side of the 

 joints. 



The filaments are elongated, simple, jointed, gelatinous and very 

 fragile, and finally separate into single joints ; each joint has two 

 opposite, bidentate angles or processes. Hence the margins of 

 the filaments are crenate, and as it is regularly twisted it not only 

 appears of unequal breadth, but the form of its joints also varies 

 as more or less of the angles is seen at the margin ; in short, as 

 they are at one time fully visible and at length entirely disappear. 



For synonyms, habitats, and description of the species, I must 

 refer to my former article on Desmidium. 



1. D. cylindricum, Ktz. Filaments subcompressed, inclosed in a di- 

 stinct mucous sheath ; joints broad as long. Kiitz. Phy. Gen. 

 p. 165. Desmidium cylindricum. Annals of Nat. Hist. vol. xi. 

 p. 373. pi. 8. fig. 1 ; Menegh. /. c. p. 204. 



Plate III. fig. 4. Didymoprium cylindricum, joint dividing into two. 



2. jD. Borreri. Filaments cylindrical, not inclosed in a sheath ; joints 

 inflated, twice as long as broad. Desmidium Borreri, Annals of 

 Nat. Hist. vol. xi. p. 375. pi. 8. fig. 4. 



Additional habitats. Ashdown Forest and near Battle, Sussex, 

 Mr. Jenner ; Ireland, Mr. Andrews. 



Plate III. fig. 5. Didymoprium J5orrm, joints dividing. 



GLiEOPRiUM, Berh. {in lit.) 



Filaments elongated, simple, cylindrical, very gelatinous ; joints 



• Read before the Botanical Society of Edinburgh, July 11, 1844. 



