262 DESCRIPTION OF [Polygastrica. 



Some species bear a considerable resemblance to species of Xan- 

 thidium, to which genus Ehi'enbcrg refers them; but in Xanthidium 

 the frond, iiTespective of the spines, is not angular in the end view, 

 and there is a projection at the centre of each segment in the front 

 view." 



Ehrenberg's characters of his genus Staurastrum or the cross-star 

 Animalcules, are their being free, and possessing a simple univalved 

 foiu-'sided lorica. They are sometimes, perhaps, developed in a 

 filiform chain. No locomotion has been observed ; indeed their only 

 resemblance to an animal, even as stated by Ehrenberg, is their in- 

 crease by self-division, though he thinks the green matter within 

 them ova. 



(A.) Frond smooth, or rough ivith mimde puncta-lilce granules ; end 

 riew with the lobes or angles inflated and mucronated or awned. 



f Frond smooth. 



STAtrRASTRTTM: dcjectum. — Segments lunate or elliptic ; constricted 

 portion very short ; end view with inflated awned lobes. 



Var. fa. J — Segments externally lunate ; awns directed outwai'ds. 



Var. fh.j — Segments elliptic ; awns parallel. 



Yar. fc.) — Awns converging. 



The conjugated fronds are connected by the formation of a bag-like 

 receptacle or cell, colourless and very thin ; into this sac the endo- 

 chrome of the two fronds passes, forms an orbicular body which 

 increases in density, becomes hairy and ultimately spinous, and con- 

 stitutes a perfect sporangium. S. dejectmn is larger than S. ciispida- 

 tum, its spines are shorter, and its segments are connected either 

 without a band, or by a very short one. Length of frond 1 -833rd. 



S. cuspidatum. — Segments fusifonn, connected by a long narrow 

 band ; awns parallel or converging, but straight ; end view with 

 3 to 4 inflated awned lobes. Length 1 -883rd. Sporangia with fewer 

 spines than those of S. dejectum. 



S. aristiferum. — Lobes in front view prolonged into mammiUate 

 awned projections which are somewhat constricted at the base ; end 

 view with 3 to 4 awned lobes. (1-65 7th.) 



S. Diekiei. — Differs from the three preceding species in its more 

 turgid sub-elHptic segments, and in the short, ciu'vcd, converging spines. 

 End view with three slight inflated mucronate lobes. (1 -855th.) 



S. hrevisjnna. — Segments turgid, elliptic, minutely mucronate; 



