SPECIES OF DESMIDS. 95 



c. Three times longer than wide, smooth; diameter y'tstt to x^rj- 

 (18-20/^) minutus, 91 



c. Four times longer than wide, smooth; diameter -j|^ (48/*) ; linear 

 elliptical, no lip penioides* 



c. Four to six times longer than wide, smooth or indistinctly punc- 

 tate; front view tapering, lateral fusiform, ^rsr '^Onrs" (20-22/*),. 



Icevis, 91 



19. Xanthidium. Fig. 19. 



§ Spines divided at the ends armatum, 92 



§ Spines subulate, ends not divided {a). 



a. Spines more or less scattered, numerous . . acicleatuin, 92 



a. " " " " 4 within the margins, Columbtanunr** 



a. Spines marginal (f). 



b. Basal angles with 2 spines (a'). 



b. " " " I spine {c). 



c. Other spines geminate in 4 pairs ... . cristatum, 93 

 c. " " " in 2 pairs on the end, single on the sides,. 



astepticm, 93 



c. " " not geminate, single on the ends . . Torreyi.*'^ 



d. Other spines 6 to 10 pairs on semi-cell; protuberance beaded, 



bisenariwn, 93 

 d. Other spines 2 to 4 pairs {e). 



d. " " none . . . tetracentrotum, 95 



e. Other spines, 4 pairs, terminal ... . . fasciculatum, 93 

 e. " " 2 pairs, basal, vertical . . reciocornutum, 94 

 e. " " 2 pairs, terminal; a row of granules above the cen- 

 tral projection, a spine above the granules, Minneapoliense, 94 



e. Other spines, 2 pairs, terminal; a row of granules above the cen- 

 tral projection, no spine above the granules . polymazum, 94 

 e. Other spines, 2 pairs, terminal, no granules above the projection 



(/)• 

 /. Diameter ^^ in. (ss-65/<) or more, Tylenanum\, fasciculatum, 93 



/. " -5^ in. (soyu) or less; semi-cell truncate-triangular, 



asteptum, 93 



/. " " " semi-cell not truncate-triangular, 



aniilopcBum, 94 



*Journ. R. Micr., Soc, Feb., 1886. 

 **F. W. Algfe, p. 34 et seq. 

 fjourn. R. Micr. Soc, Dec, 1885. 



