10 Mr. J. Ralfs on the British Desmidiez. 
the oral appendages. That it is a member of the Aphroditacee 
noone 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. 
Prare 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. } 
IIL.—On the British Desmidiee. By Joun Ratrs, Esq., 
M.R.C.S., Penzance *, 
| With a Plate. ] 
Divymorrivm, Kitz. 
Filaments elongated, gelatinous, fragile, eylindrical 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. pl. 8. fig. 1; Menegh. J. ¢. p. 204. 
Prate III. fig. 4. Didymoprium cylindricum, joint dividing into two. 
2. D. 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. pl. 8. fig. 4. 
Additional habitats. Ashdown Forest and near Battle, Sussex, 
Mr. Jenner; Ireland, Mr. Andrews. 
Prare III. fig. 5. Didymoprium Borreri, joints dividing. 
Gixoprium, Berk. (in hit.) 
Filaments elongated, simple, cylindrical, very gelatinous ; joints 
* Read before the Botanical Society of Edinburgh, July 11, 1844, 
