SPECIES OK DESMIDS. I05 



s. Diameter -j-J-^- in. (3i/<) or smaller (t). 

 s. " ^ in. {60/u) or longer («). 



/. End straight, sides tapering into short, mostly obtuse processes, 



triconie, 126 



/. End convex; processes short, stout . . . . crenulatum, 126 



/. End concave; processes short, upwardly diverging, 



pusillnm, 130; Donnellii; 132 



u. Processes short, robust, incurved; end of semi-cell truncate, 



cerastes, 133 

 u. " long, narrow, incurved; end of semi-cell convex, 



ankyr aides, it,i 

 u. Processes long, horizontal . . . . ' . tetracerum, 134 



V. Processes curved, apices bifid . . pentadadum, 129 



V. " " apices entire . .... incisum, 132 



V. Processes horizontally radiating; ends of cell with bifid papillae, 



pentaceruni; 134 

 V. Processes horizontally radiating; ends without papillae, 



crenulatum, 126 

 V. Processes upwardly diverging, the apices bifid . franconium, 131 

 w. Diameter -g-l-j in. (40 /t) or smaller (x). 

 «'■ " -Fir in- (7°/^) or larger {y). 



X. Isthmus centrally ribbed; rays curved downward . comptum, 129 

 X. " not ribbed; in end view rays basally separated by an 



acute incision .... incisum, 132 



X. Isthmus not ribbed; in end view rays separated by a rounded 



sinus . .... . crenulatum, 126 



y. End with prominent papillae; diameter ^^-j- to y^ in. (140-150/^), 



^ Ophiura, 134 



y. End with prominent papillae; diameter -j-^j to -g-^-j in. (7S-85yu), 



coronulatum, 135 

 y. End without prominent papilla; ray margins serrate, 



macrocerum, 134 

 y. " " " ray margins granulate-crenate, 



hexacerum, 137 

 z. End view oval, ends produced in a long, thin arm, ungulatum, 136 

 z. " fusiform . . fusiforme, 137 



z. End view triangular or 3-radiate {aa). 

 z. " 4-radiate or angular [ee). 

 z. " 5-radiate {ff) 



