BRITISH DESMIDIE^. 201 



11. Staurastrum. 



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

 Frond either rough, spinous, or with elongated angles 5 



2. Angles with a minute nipple-hke projection 3 



Angles rounded, without a projection 4 



3. Sides convex tumidum. 



Sides concave brevispina (d. 



4. Segments elliptic in the front view muticum. 



Segments semiorbicular in the front view orbiculare. 



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



Frond either awnless or having 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 without a band 8 



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



Awns, in front view, not terminating lobes 9 



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



turgid dejectum. 



Awns curved and convergmg ; 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, spmous or dentate ; divided processes, 



if any, rough 13 



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

 End view vdth short geminate processes from each lobe ........ l(sve. 



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



view broadly rounded and entii'e 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-triangular ; end view of frond with convex sides, muricatum. 

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



concave sides hirsiituin. 



Spines thorn-like ; end view of frond with very concave sides, teliferum. 



16. Segments quadrangular in the front view quadrangular e. 



Segments not quadrangular in the front view 17 



