DesmidiecB.'] infusorial animalcules. 261 



they can have no place, the descriptions given are totally insufficient 

 to discover theii- true generic affinity, and we arc consequently com- 

 pelled, for facility of reference to Ehrenberg's descriptions, to intro- 

 duce them in the present inappropriate place, or otherwise to insert 

 them in an appendix. 



AnTHEODESMUS Tceuia. — "Wands narrow, ilexihle, nearly eight 

 times longer than broad, and smooth. Has the habit of A. striatulus, 

 but is more slender. 



A. striatulm fFragilaria striatulus, Lyngbye.y — Met with in long, 

 soft, green, but not siliceous chains, resembling Fragilaria rhabdosoma. 

 Width of chain 1-5 76th. 



Genus Staukasteum. — Frond simple ; constiicted at the middle ; 

 end view angular, or circular with a lobato-radiate margin, or, rarely, 

 compressed with a process at each extremity. Frond mostly minute; 

 the segments generally broader than long, slightly twisted, and in 

 many species elongated laterally into a process, so that the con- 

 striction on each side is a roundish or angular sinus ; in other 

 respects the front view shows the segments quite entire, The end 

 view varies in form : in most of the species it is triangular or 

 quadrangular, and the angles are either rounded or elongated into 

 rays ; in some it is circidar, with five or more processes, forming 

 marginal rays ; in a few species it is compressed, and the extremities 

 tei-minate by a process. 



" Ehrenberg has distributed the Staurastra among different genera, 

 according to the number of angles or processes seen in an end view. 

 Thus he refers those with three angles to Besmidium, and those with 

 foiu" to Staurastrum ; and he formed his genus Pentasterias for the 

 reception of an organism with five rays. But this arrangement 

 appears unnatural; not only because it separates nearly allied forms, 

 but also because the number of rays is not constant even in the 

 same species. I have generally found the Pentasterias ma/rgaritacea 

 (Ehr.) with six rays, although not unfrequently with five, and occa- 

 sionally with seven rays to a segment. Staurastrum contains more 

 species than any other genus hi the family : their forms are in great 

 variety, and but little affinity can be traced between many of them. 

 Sjmrangia generally spinous. Staurastrum differs from Besmidium 

 in never forming a filament; and from Arthrodesmus and Cosmarium, 

 by its angular shape, or by having the ends elongated into processes. 



