PROCEEDINGS OF SOCIETIES. 189 
nator by reflecting the light from a lateral opening down through 
the object-glass. 
Mr. Porte exhibited a series of slides of vegetable sections 
showing a variety of spiral vessels. 
Dr. Moore showed a Scytonema, the same as the one sent by 
him to Dr, Hassall, and named by the latter S. hibernicum. 
Dr. Moore had taken this on the occasion of the Lugnaquilla 
excursion. 
February 15th, 1866. 
Dr. E. Perceval Wright brought forward a number of diatoms 
from Mauritius, collected by Captain Crozier, R.E. These Mr. 
O’Meara undertook to examine and report upon. 
Mr. Archer exhibited side by side on the same slide two rare 
species of Staurastrum. These were Stawrastrum oligacanthum 
(Bréb. in litt.) and Stawrastrum (Phycastrum, Pachyactiniwn) 
cristatum (Nag.)=Staurastrum nitidum (Arch.). He brought 
them forward, however, chiefly for the purpose of drawing atten- 
tion to their marked distinctions, and yet to the possibility of 
their being mistaken the one for the other. The first species he 
had seen only a very few times (see Minutes of Club of June 
15th, 1865), the second only from the pool in which these speci- 
mens were found ; but in this he had taken it for three or four 
successive years. It is not easy to bring the distinctive characters 
of these two forms before other observers without the specimens, 
but yet Mr. Archer thought no two could be more distinct. In 
fact, with an inch object-glass one could distinguish them, once 
their characteristics have been seized upon. In front view S¢. 
cristatum has its ends convex, the lateral extremities sub-mammil- 
late, and the end view has the sides convex. In St. oligacanthum 
in front view the ends are flat, the lateral extremities subacute; 
in end view the sides concave at the middle, the angles inflated, 
then acute. 
The Rev. E. O'Meara, A.M., showed a new Striatella found by 
him on a frond of Haloplegma Preissii from Australia. As only 
two other species of this genus are already known, this acces- 
sion would possess an additional interest. The characters of the 
genus are stipitate, septate, the septa alternate, and not extending 
across the valve. By such peculiarities, the form under considera- 
tion would be at once recognised as a Striatella, of which genus 
Mr. O’Meara felt himself quite warranted in regarding it as a new 
species. In Striatella unipunctata the stipes are remarkably long ; 
the septa rectilinear, with bead-like expansions at the distance of 
about ird the length of the frustule from the margin. In the 
form under consideration the stipes are not remarkably long; - 
the septa are curvilinear, and curved in opposite directions in the 
VOL. VII.—NEW SER. ) 
