254 
PROCEEDINGS OE SOCIETIES. 
Staurastrum O'Mearii (n. s.). 
Frond very minute; segments smooth, ends truncate (in the quad- 
rangular variety slightly convex); central constriction not deep, forming 
an obtuse angle; constricted portion very short; a single awn at each 
angle; awns diverging in the front view, acute. 
End view quadrangular or triangular; sides straight;^ angles not 
inflated. 
Sporangium orbicular, spinous; spines at first subulate, afterwards 
slightly inflated at the base, acute. 
Length of frond of quadrangular variety, TsVe th of an inch; breadth 
at end (exclusive of spines), asV»; diameter at isthmus, tyTu', length of 
spine, seVo- 
Length of frond of triangular variety, t?V oth of an inch; breadth at 
end (exclusive of spines), iioo; diameter at isthmus, stoo ; length of 
spine, 3 *W 
Diameter of sporangium, without including spines, ttz oth of an inch; 
including spines, -rluth of an inch. 
It is with very great pleasure I am permitted to call this species after 
my friend the Eev. Eugene O’Meara, to whom I trust it may afford some 
gratification to have his name associated with this species of a group 
kindred to his favourite and beautiful Diatomaceae. 
There remains one other new species which it becomes my duty to 
bring forward and describe, which, owing to its elongate form, and not 
being at all constricted, and its entire segments, at once takes its place 
in the genus Penium.f It is in size about equal to Penium Brebissonii, 
but otherwise not at all resembling that species. Its outline is broadly 
spindle-shaped or fusiform, tapering pretty quickly to the ends, with 
cuneate segments, which are bluntly and roundly pointed, and it presents 
always the same form when made to roll over. The endochrome is gra¬ 
nular, and bright green, with a transverse, rather sharply defined, pale 
band at the centre; and usually has immersed in each half a single 
central corpuscle. Close to each end there exists a smoothly and sharply 
defined, perfectly circular cavity, excavated, as it were, out of the endo¬ 
chrome, in which there are two or three active granules, as in Closterium 
(see Fig. 14). The endochrome sometimes appears as disposed in longitu¬ 
dinal fillets, but more frequently this is not evident. The drawings repre¬ 
sent this fully as marked as I have noticed it. The mode of division in this 
form appears to follow that in Closterium, by a separation of the contents 
and external constriction. Fig. 15 represents this process half accomplished. 
* I fear the figures (Figs. 9, 11) may convey the idea of the sides being somewhat 
concave : they are quite straight, and have the angles tipped merely with an awn. 
f The description of this species of Penium having been written since this paper was 
read, and since the former part of it went to press, the “ heading” includes only four new 
species, instead of five; but I have, nevertheless, introduced it, anxious to take advan¬ 
tage of the Plate. 
