O’Mrara—Report on the Irish Diatomacee. 279 
point. The striation of the valves formed of moderately scattered 
granules, arranged in curved radiating lines, slight or absent ; about the 
middle point, more robust, and consisting of angular granules arranged 
in three or four longitudinal lines, and in short transverse lines diverg- 
ing towards the suture, or that portion of the side-surface of the valve 
which lies between each pair of ae vealed Granules about 22 in 
0.05™" along the suture; striation of the connecting-zone unknown ; 
length of the side of the basal surface = 0:°055™™ -— 0°175™™.” 
This beautiful form I considered to be an undescribed species of 
Triceratium, until I saw Heiberg’s figure of Trinacria regina, when I 
at once recognised its identity. (PI. 27, fig. 14). 
Heiberg, De Danske Diat., p. 50, T. in., fig. 7. 
Arran Islands, Co. Galway. 
In reference to the locality of this form, Heiberg says:—‘“‘ It 
occurs abundantly in the brown Moleer from Fuur, in which it is one 
of the most common forms. In the white Moleer I have found only 
a few single specimens.” It is then a matter of interest to discover 
it on our own coasts. 
Famrry IV. ISTHMIEA, Agardh. 
Frustules trapezoidal on front view, on the side view broadly 
elliptical, without processes; one valve having the extreme corner 
produced, at the end of which is secreted the mucous cushion by which 
frustule is united to frustule, so as to form an irregularly branched 
filament. 
In a classification founded on the symmetrical or unsymmetrical 
shape of the frustule, this family should in strictness be assigned to a 
different position; but I place it here not only in deference to the 
views of all authors known to me, but because in point of fact 
it presents considerable analogy to the Biddulphiew, and without 
violence could not be suitably placed at a distance from that 
group. 
Genus I. Isrumta, Agardh. 
Characters of the Genus those of the Family. 
Isthmia nervosa, (Kiitz.) Marine. 
Striation of valves areolate; areoles large, close, somewhat hexa- 
gonal, with numerous strong anastomosing coste springing from the 
margin, and disappearing towards the middle of the valve; connecting 
membrane areolate, areoles much smaller than those on the valve 
(Pleo, fie bo.) 
Kutzbac, p. lor, rb. xix. fie. 5.” Wm. Sm., B.-D., Vol. iz, 
