QONIOCYSTIS. 351 



and formation of sporangia in this species, resulting as mother 

 Desmidece from the union of the endochromes 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 

 TyndaridecB 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- 

 liferce to present an appearance exactly similar, a fact which 

 has not escaped the attention of Mr. Thwaites. 



3. TRIGONOCYSTIS MUBICATA Hass. 

 Plate LXXXIV. Fig. 9, 10. 



Char. Fronds muricated, deeply constricted, transversely el- 

 liptic. Segments approximate. End view triangular, with 

 convex sides. 

 /3 Fronds furnished with short spines. 



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

 Breb., Alg. Fal. p. 66. (1835). Desmidium apiculosum 

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

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

 dium deltoideum Corda, Observ. Microscop. sur les Aui- 

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



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

 Hants ; Kackham Common, near Pulborough ; Pilt- 

 down Common, near Uckfield ; Mayfield and Heathfield. 

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

 Ralfs. /3. Sussex: Mr. Jenner. Dolgelly: Mr. Ralfs. 



From Staurastrum 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. 



