BRITISH DESMIDIEiC. 201 



11. Staurastrum. 



1 . Frond neither rough nor spmous ; angles in end view broadly rounded. 2 

 Frond either rough, spinous, or with elongated angles 5 



2. Angles with a minute nipple-like projection 3 



Angles rounded, without a projection 4 



3. Sides convex tumidum. 



Sides concave hrevispina (3. 



4. Segments elliptic in the front view niuticum. 



Segments semiorbicular in the front view orbiculare. 



5. Frond with awned inflated angles, but without other spines 6 



Frond either awnless or ha\ang other spines besides the awns .... 11 



6. Frond rough with minute granules lunatum. 



Frond smooth 7 



7. Segments connected by a ribbon-like band cuspidatum. 



Segments connected vdthout a band 8 



8. Awns, in front view, terminating conical lobes aristiferum. 



Awns, in front view, not terminating lobes 9 



9. Awns straight, rarely converging ; segments, if elliptic, not 



turgid dejectum. 



Awns curved and converging ; segments turgid-elliptic 10 



10. Segments inflated ; awns inconspicuous brevispina. 



Segments turgid ; awns distinct Bickiei. 



1 1 . Frond smooth, glabrous ; angles prolonged into processes 



divided at the apex 12 



Frond either rough, spinous or dentate ; divided processes, 



if any, rough 13 



12. End view with an elongated process from each angle .... brachiatum. 

 End view with short geminate processes from each lobe Iceve. 



13. Frond with simple, acute, uniform spines; angles in end 



view broadly rounded and entire 14 



Frond, if spinous, either with some or all of its spines not 



subulate, or with angles not rounded in the end view 16 



14. Segments quadrangular in the front view Hystrix. 



Segments semi-orbicular or reniform in the front view 15 



15. Spines conico-triangiUar ; end view of frond with convex sides, murieatum. 

 Spines hair-like ; end view of frond with convex or slightly 



concave sides hirsutum. 



Spines thom-hke ; end view of frond with very concave sides, teliferum. 



16. Segments quadrangular in the front view quad r angular e. 



Segments not quadrangular in the front view 17 



