82 ARCHER AND DIXON, ON DESM1DIACE.E. 



and parallel in their direction with those of the opposite seg- 

 ment; the end lobe expanded laterally into two attenuated 

 projections, which are horizontally disposed, and parallel in 

 their direction with that of the basal lobes, so that the entire 

 frond is of a pinnatifid character; the ends of the fronds 

 convex, straight, or having at the middle a very slight con- 

 cavity or depression, not emarginate. 



Tetrachastrum mucronatum (sp. nov.) 



Specific characters : Frond longer than broad ; ends 

 rounded, having a slight central concavity; end lobe having 

 its lateral projections terminated by a mucro ; basal lobes 

 broadly and bluntly triangular, having at their magin at each 

 side either one, two, or three minute mucro-like spines ; 

 empty frond punctate, the puncta scattered. 



Symbol : ab, c, parallel {vide supra) . 



Locality : Bog near Carrickmore, Co. Tyrone. 



Measurement : Length of frond, T | T ; greatest width, ^j ; 

 width of neck, ^3- ; diameter at constriction, 5 ^ ; greatest 

 depth, ^3.3 of an inch. 



Plate VII. — Fig. 5, front view with endochrome ; fig. 6, 

 empty frond; fig. 7, outline of side view; fig. 8, outline 

 of transverse view. 



General description : The frond in this species is large, 

 smooth, entire, about one fourth longer than broad; in the 

 front view divided into two segments by a deep constriction, 

 forming an acute-angled straight-sided notch, not linear, but 

 broadest at the outside. The segments are constricted about 

 two thirds of the way from the base by a rounded sinuosity, 

 causing the basal lobes to be of a bluntly triangular outline, 

 straight on the lower, turgid or convex on the upper margin, 

 and furnished thereon with one, two, or three minute mucro- 

 like spines, one always at each basal angle. The basal lobes 

 slope upwards to form a broad neck, uniting the terminal Lobe 

 to the basal portion : supposing the end to be absent, the 

 frond would be orbicular. The lateral projections of the end 

 lobe have their extremities tipped by a mucro, and somewhat 

 projected downwards. Ends of the fronds convex with a 

 gentle central concavity. In the side view the frond is 

 smooth, about four times longer than its greatest depth ; the 

 central constriction is rather deep; the segments in this view 

 ovate, turgid near the constriction, somewhat tapered towards 

 the ends, which are rounded. The transverse view is broadly 

 fusiform; the endochrome rich green, with scattered granules. 

 The empty frond is punctate, the puncta scattered. 



