GONIOCTSTIS. 351 



and formation of sporangia in this species, resulting as in other 

 DesmidccB from the union of the cndoclu'omes of two cells, 

 which in them is never effused from one cell into another, 

 but always into a distinct receptacle intermediate between 

 the two fronds: this is also the case in certain species of 

 Tyndarideoi and Mesocarpi amongst the Conjugates. 



The sporangia in T. mucronata are circular and smooth, 

 and at first enclosed in a membrane larger than itself, this 

 gradually disappears, and the sporangium becomes spinous, 

 in which state it bears some resemblance to a Xanthidium. 

 I have observed occasionally the sporangia of the Vesicu- 

 lifer<2 to present an appearance exactly similar, a fact wliich 

 has not escaped the attention of Mr. Thwaites. 



3. Trigonocystis muricata Hass. 



Plate LXXXIV. Fig. 9, 10. 



Char. Fronds muricated, deejjly constricted, transversely el- 

 liptic. Segments approximate. End view triangnlar, iciih 

 convex sides. 



/3 Yvonds fur 7iished with short spines. 



Meneghini, Synops. Desmid. p. 266. Binatclla muricata 

 Breb., Alg. Fal. p. QiQ. (1835). Desmidium apiculosum 

 Ehr., Infus. p. 142. ; Ralfs, in Annals, vol. xv. p. 154. 

 pi. xi. fig. 1.; Jenner, in loc. cit. p. 194. — /3. Xanthi- 

 dium deltoidcum Corda, Observ. INIicroscop. sur les iVui- 

 malc. de Carlsbad, p. 29. pi. v. figs. 38, 39. 



Hab. In small pools ; Cheshunt : A. H. H. "Weston Bogs, 

 Hants ; Rackham Common, near Pulborough ; Pilt- 

 down Common, near Uckfield ; Mayfield and Heathficld. 

 Sussex : Mr. Jenner. Dolgelly and Penzance : Mr. 

 Ralfs. — /S. Sussex: Mr. Jenner. Dolgelly: Mi-. Ralfs. 



From Sfaurastr7nn tricorne this species may be at once dis- 

 tinguished by the convex sides of the segments in the end 

 view, and by the adult fronds being not merely muricated 

 but spinous. The variety is probably distinct. 



