18 Transactions of the Society. 



gpicuous, separating the two frustiiles widely from one another, 11 /x 

 long by 6 /i wide, quite colourless. Cell-membrane punctate, and with 

 five distinct protuberances in each frustule. 



Bog pools, Eoche and St. Denis. Nearest to G. excavatum Nordst., 

 but larger ; G. Fortianum Arch, belongs also to the same section. 



*Cosmarium bioculatum Breb. Bog pools, not unfrequent. 

 „ moniliforme Turp. 



* „ Meneghinii Breb. Bog pools, Eoche and St. Denis. 

 ,, AVittrochii Lund. 



Xanthidium aculeatum Ehrb. 

 „ fasciculatum Ehrb. 



* „ cristatum Ehrb. var. a Ealfs. Frequent. 



This species is well distinguished by the solitary basal spine, which 

 is, however, frequently rudimentary or altogether wanting. 



Staurastrum dejectum Breb. 

 „ Dickiei Ealfs. 



„ muticum Breb. 



„ teliferum Ealfs. 



„ Pringsheimii Eeinsch. 



„ alternans Breb. 



*Staurastrum (Didymocladon) cornubiense n. sp. Fig. 24. 



Frond minute, 35 yu, long, 28 ^u, broad. Each frustule elHptical, but 

 with the lower edge flatter than the upper rounded edge, 2-3-dentate at 

 the base, and with a bifurcate colourless process on the shoulder. In 

 front of each frustule is a large ovate protuberance, much deeper green 

 than the rest of the frond, ending in two bifurcate horns, 14 fju long 

 including the horns, 7 • 5 /i broad. 



Bog pool, Eoche, occasional. Belongs to the section (Kalfs's genus 

 Didymocladoji) in which each frustule is furnished with bifurcate pro- 

 cesses. It is considerably smaller than most of the section, resembling 

 most nearly, in this and other respects, S. ;pseudofurcigerum Eeinsch, 

 but the very remarkable urn-shaped protuberance well distinguishes it 

 from all other forms yet described. 



Staurastrum polymorphum Breb. 

 „ gracile Ealfs. 



* „ cyrtocerum Breb. Bog pool, Mawgan. 



* „ paradoxum Mey. Bog pools. 



* „ tetracerum Ktz. Bog pools. 

 Arthrodesmus Incus Breb. 



„ convergens Ehrb. 



Zygnemacks:. 

 Spirogyra porticalis Vauch. 

 „ longata Vauch. 



* „ nitida Dillw. Mill-dam, vaUey of the Gannel, and 



elsewhere, frequent. 

 *Zygnema insigne Hass. With the preceding. 



„ Hassallii Benn. ? {Z. anomalum Cooke). Not seen 

 in conjugation. 



