1 70 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



6; G. S. West, 1905, p. 287. Cells perfectly ellipsoid, about 

 12X5 p-, 4 in a single series, 2 strong spines, curved outward, on 

 each terminal cell ; the two median cells with one such spine 

 each, in opposite directions. Barbados. Madagascar. 



14. CRUCIGENIA Morren, 1830, p. 404. 



Colonies free, of 4-8-16, rarely more cells, lying in the same 

 plane, with perforations at places where the cells have divided 

 and separated from each other ; cells with parietal chromato- 

 phore and one pyrenoid, smooth or with prominences, touching 

 at the middle or at the outer end, and enclosed in more or less 

 plentiful gelatine ; asexual reproduction by the division of a 

 cell into 4 daughter cells, arranged like the mother colony. 

 Fresh water plankton algae. 



KEY TO THE SPECIES OK CRUCIGENIA. 



i. Cells apiculate. 3. C. apiculata. 



i. Cells not apiculate. 2. 



2. Cells ovoid, oblong, or somewhat curved, 4-32 in a colony. 



i. C. rectangularis. 

 2. Cells rhomboidal, 4 in a colony. 2. C. crucifera. 



1. C. RECTANGULARIS (A. Br.) Gay, 1891, p. ioo, PL XV, 

 fig. 151 ; Wittr. and Nordst., f Alg. Exsicc., Nos. 53, 171. Cells 

 4-6X5-7 /", 4-8-16-32 in a colony, 13-55 ^ square, with rounded 

 angles ; always in groups of 4, with a quadrangular opening 

 in the center of the group ; fragments of the mother cell wall 

 sometimes persistent ; cells oval or oblong, touching near the 

 outer end, or curved and touching near the middle. Fig. 54. 

 Greenland, Mass. Europe, Asia. 



2. C. crucifera (Wolle) nov. comb.; Staurogenia-crutiata 

 Wolle, 1887, p. 171, PI. CI/VII, figs. 9-n. Cells rhomboidal, 

 equilateral, -with incurved sides and rounded angles, four form- 

 ing a colony of the same form as the individual cell; "cells 

 with a cruciform marking on the surface." Wolle. Pa. 



The figures given by Wolle are very rudimentary, but seem 

 to indicate a distinct species. The cruciform marking of the 

 cells is probably due to cell division in process. 



3. C. APICULATA (L-emmermann) Chodat, 1902, p. 207 ; 

 Snow, 1903, p. 376, PL I, fig. V. Cells elongate, ovoid, 

 or by pressure at one end subtriangular, 5-8X3-5 p-, with an 

 apiculum at one end, sometimes at each end ; united in fours or 

 multiples of four in a flat, more or less regularly rectangular 

 plate. 



In reproduction each cell divides to form 4 daughter cells, 



