SPECIES OF DESMIDS. 95 



c. Three times longer than wide, smooth; diameter T -jfa to i J 

 (i8-2o/*) minutus, 91 



c. Four times longer than wide, smooth; diameter -^ (48/^)5 linear 

 elliptical, no lip penioides* 



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

 tate; front view tapering, lateral fusiform, i ^ 1 go tOy^-^ (20-22^),. 



Icevts, 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 . . . aculeatum, 92 



a. u 4 within the margins, Columbianum'** 



a. Spines marginal (b\ 



b. Basal angles with 2 spines (J). 



b. " " i spine (c). 



c. Other spines geminate in 4 pairs cristatum, 93 



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



asteptum, 93 



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



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



bisenarium, 93 

 d. Other spines 2 to 4 pairs (<?). 



d. " " none tetracentrotum, 95 



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



e. " " 2 pairs, basal, vertical .... rectocornutum, 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 



(/)- 



f. Diameter ^-^ in. (55-65^) or more, Tylerianum\ t fasciculatum, 93 

 /. " -5^- in. (50/1) or less; semi-cell truncate-triangular, 



asteptum^ 93 

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



antilopceum, 94 



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

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

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



