O'Meara — Report on the Irish Biato^nacece. 279 



point. The striation of tlie Talves formed of moderately scattered 

 granules, arranged in curved radiating lines, slight or absent ; ahout the 

 middle point, more robust, and consisting of angular granules arranged 

 in three or four longitudinal lines, and in shoi-t transverse lines diverg- 

 ing towards the suture, or that portion of the side-surface of the valve 

 which Kes between each pair of end-processes. Granules about 22 in 

 0.05""" along the suture ; striation of the connecting-zone unknown ; 

 length of the side of the basal surface = O-OSS"""" - 0-175""." 

 This beautiful form I considered to be an undescribed species of 

 Triccratium, until I saw Heiberg's figure of Trinacria regina, when I 

 ^t once recognised its identity. (PI. 27, fig. 14). 

 Heiberg, De Danske Diat., p. 50, T. iii., 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. 



Fa^^iixt IY. ISTHMIE^, 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 fnistule, 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 

 diflterent 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 Biddulphiea?, and without 

 violence could not be suitably placed at a distance from that 

 .group. 



Genus I. IsiHiriA, Agardh. 

 Characters of the Genus those of the Pamily. 



Isthnia nervosa, (Kiitz.) Marine. 



Striation of valves areolate ; areoles large, close, somewhat hexa- 

 gonal, with numerous strong anastomosing costae springing from the 

 margin, and disappearing towards the middle of the valve ; connecting 

 membrane areolate, areoles much smaller than those on the valve 

 (PL 27, fig. 15.) 



Kiitz. Bac, p. 137, T. xix., fig. 5. Wm. Sm., B. D., Yol. ii., 



