SOME NORTH AMERICAN DESMIDIE.E. 20,3 



139. Staurastrum parvulum, nov. sp. (PI. XVII. fii,^ 1.) *S'. minutum, psene 1 J-plo 

 longius quam latius (sine process! bus), modice constrictum, sinu aperto; semicellulfc 

 rectangulares, lateribus apicibusque leviter concavis, angulis superioribus in processus 

 longos arcuatos tenues minute nodulosos productis, apicibus minutissinie tridenti- 

 culatis, cum spina singula minuta ad angulum basalem sub processu unoquoque ; a 

 vertice visse triangulares, lateribus subrectis, angulis in processus longos hypocyrto- 

 cerosos productis, denticulo minutissimo ad basin processus uniuscujusque utrobique. 



Long. 11*5 jj. ; lat. sine proc. 8 /a, cum proc. 25-26'5 /a ; lat. istbm. 4.'5 ;x. 



This little species does not appear to be very closely related to any other. The small 

 spines at the basal angles and directly under each process are best seen when the plant is 

 somewhat tilted. 



140. S. GENTJFLEXUM, nov. sp. (PL XVII. fig. 2.) S. parvum, paulo longius (pi;im 

 latius (sine processibus), ad medium modice constrictum ; semicellulae cyatbiformes, 

 apicibus subrectis, angulis superioribus productis divergentibus subito genuflexis in 

 processus longos tenues attenuatos convergentes undulatos productis, apicibus 

 subobtusis ; a vertice vis8B triangulares, lateribus rectis, angulis in processus longos 

 subeurvatos undulatos productis ; membrana glabra. 



Long. 13*5 ^ ; lat. sine proc. 11 jj. ; lat. cum i3roc. 10 />c ; lat. isthni. 5 ^. 



111. S. SUBGRACILLIMUM, nov. sp. (PL XVII. figs. 3, 1.) S. parvum, ciiciter tarn 



longum quam latum (sine processibus); semicelluloB late cuneatae, lateribus rectis, 



apicibus retusis, angulis superioribus in processus longos horizontales non attenuatos 



minutissime undulatos productis ; a vertice vises triangulares lateribus levissime 



concavis, angulis in processus longos productis, apicibus processuum a dentibus 



subpatentibus incurvatis tribus instructis ; processi!)us unius semicelluke cum iis 



alterius alternantibus ; membrana gla])ra. 



Long. 10"5-11"5 y. ; lat. s. proc. 10-11 ^, c. proc. 54-60 ^ ; lat. isthm. 4'8-5'5 jm. 



On seeing but two specimens of this w^e placed it as a variety of *S'. gracillimum, West 



& G. S. West (in Trans. Linn. Soc. ser. II., Bot. v. (1895) p. 75, pi. 8. fig. 31), 



but after seeing many more examples, and finding its characters constant, we thought 



it advisable to regard it as a distinct species. The processes are of a different nature 



from those of S. gracilUmum ; they are less attenuated, very minutely nodulate, and the 



apices are not deeply bifurcate, but furnished with three spreading incurved teeth. 



In the front view the processes are almost horizontal and the teeth at their apices are 



seen to be in one plane, the apex of the semicell is concave, and in vertical view the 



sides are very slightly concave or almost straight. 



142. S. AsTEROiDEUM, nov. sp. (PL XVII. fig. 5.) S. parvum, paulo latius quam 

 longius (cum processibus), modice constrictum; semicellula? quadrato-cuneatcC, 

 apicibus convexo-truncatis, angulis superioribus in processus bi- vel trinodulosos 

 leviter curvatos extrorsum productis, apicibus tridenticulatis ; a vertice visic 5-radiatte, 

 processibus tarn longis quam diameter corporis ; membrana glabra. 

 Long. s. proc. 15-16-5 ^, c. proc. 19-24 ^ ; lat. s. proc. 8-5-10-5 ^, c. proc. 25-27 ^ ; 



lat. isthm. 5*5 u. 



^ 2o2 



