1 66 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



the number and size of the angular projections ; all passing 

 into each other without any sharp line. 



8. THAMNIASTRUM Reinsch, 1888, p. 513. 



Cells solitary, free, composed of six branches issuing at right 

 angles from a common center, di-trichotomously divided ; ulti- 

 mate divisions acute, spreading. Only one species. 



T. CRUCIATUM Reinsch, 1888, p. 513, PI. VIII, fig. 3. Char- 

 acters of the genus; ultimate divisions 100-200, 1-2 ^ diam. 

 Fig. 49. Mass. 



Nothing being known as to the reproduction of the plant, 

 which has not been reported since its original discovery, its 

 position here is provisional only, and based on habit characters. 

 9. CERASTERIAS Reinsch, 1867, p. 68. 



Cells solitary, free, consisting of elongate rays from a com- 

 mon center, without distinct central body ; otherwise as in Tet- 

 raedron. 



Doubtfully distinct from Tetraedron, differing only in the 

 greater development of the projections and consequent reduc- 

 tion of the main body. 



KEY TO THE SPECIES OF CERASTERIAS. 



i. Rays acute. i. C. raphidioides. 



i. Rays obtuse. 2. C. stattrastroides. 



1. C. RAPHIDIOIDES Reinsch, 1867, p. 68, PI. V, fig. i ; 

 1888, p. 511. Rays 3-8, subulate, acute. Fig. 48. With many 

 forms, of which we have two. 



Var. INCRASSATUM Reinsch, 1888, p. 512, PL VIII, fig. 4 L 

 Cell consisting of 4 or 5 rays, 2.5-3X10-15 /n, 3 or 4 arranged in 

 a whorl at one end of the other ray ; or 2 or 3 in a whorl about 

 one continuing the direction of the single ray, the single ray 

 acuminate, other rays equal with rounded or sometimes acumi- 

 nate ends. Mass. Europe, Africa. 



Var. INAEQUALE Reinsch, 1888, p. 512, PI. VIII, fig. 4, a-c. 

 Single ray 10-15X2-3 n, with acute lower end, at upper end with 

 3 similar acute rays, and 3 rays of about half the length, with 

 obtuse ends. Mass. Europe, Africa. 



2. C. STAURASTROIDES W. and G. S. West, 1895, p 268, 

 PI. XIV, fig. 16. Rays four, elongate, attenuate, minutely 

 granulate, apex obtuse; thickness of central portion, 9-10 /*; 

 total diam., 30-35 p.. On trees. Dominica. 



Polyedrium minutum L,arsen, p. 104, fig. 7, would seem to be- 

 long here, apparently intermediate between the two species. 



