26 One Thousand Objects 



or four equidistant rays, each terminated by a spur or 

 spine. A common species. (PI. III., fig. 15.) 



187. ALTERNATE STAURASTRUM (Staurastrtim alter- 

 nans). The two segments are oblong, and rough on the 

 surface, but, not lying in the same plane, have the appear- 

 ance of being unequal. End view three-lobed, the lobes 

 of the one segment alternating with the lobes of the other. 

 Not so common as the last. (PI. III., fig. 16.) 



1 88. FINGER-LIKE PENIUM (Penium digitus). Of a 

 long elliptic form, with nearly straight sides and rounded 

 ends. The division into two segments is indistinct, but 

 there is a paler band across the centre. End view circu- 

 lar. A very common species. (PI. III., fig. 18.) 



189. BREBISSON'S PENIUM (Penium Brebissonii}. This 

 is scarcely so large as the last, and the sides are straighter, 

 so that it has the form of a cylinder with rounded ends. 

 It is often so plentiful in places where water lodges in wet 

 weather as to form a stratum. (PI. III., fig. 19.) 



190. CAPPED TETMEMORUS (Tetmemorus gramilatus). 

 This genus at first sight resembles the last in its cylin- 

 drical form and elongated fronds, but it differs in being 

 constricted at the middle and in having notches at the 

 ends. The present is the most common species, which is 

 spindle-shaped, with colourless ends. 



191. SLENDER DOCIDIUM (Docidium baculum} consists 

 of long, straight, slender, thread-like fronds, divided across 

 the centre into two segments, each of which is a little 

 swollen near the joint. There are several species belong- 

 ing to the same genus, but this is the most common. (PI. 

 III., fig. 20.) 



192. CRESCENT CLOSTERIUM (Closterium litnuhi). 

 This species and the four following belong to a genus in 

 which the fronds are narrowed towards each end, and 

 curved like a bow or a crescent. In this, one side is 

 nearly straight, and the other tapers rapidly from the 

 centre towards each end. (PI. III., fig. 21.) 



193. EHRENBERG'S CLOSTERIUM (Closterium Ehren- 

 bergii] differs from the last in being more curved, the 

 lower side concave instead of straight, and a little swollen 



