O'Meara — Beport on the Irish Diafomacecp. 271 



Systephania anglica, Donkin, Q. J. M. S., 1861, p. 12, PI. i., 

 fig. 14. 



Stomaclis of Ascidians, Eoundstone Bay, Co. Galway. ' 



Odontodisciis hilernicus. !N". S. Marine. 



Disk about "0018 in diameter; areolate ; areoles round, decussately 

 arranged, reaching the circumference ; teeth more numerous than in 

 former species, and shorter. (PI. 27, fig. 7.) 



Stomachs of Ascidians, Eoundstone Bay, Co. Galway. 



A. Frustides symmetrical. Valves not circular. 



Family II. BIDDIJLPHIE^, Kiitz. 



Yalves lanceolate, in some cases nearly orbicular, furnished with 

 distinct processes and spines ; connecting zone largely developed in 

 full-grown specimens. In such species as have been seen in a living 

 state the frustules are united in filaments. 



This group, established by Kiitzing without any very distinct defini- 

 tion, embraced the following genera, Isthmia, Odontella, Biddulphia, and 

 Zygoceros. Ealfs, in Pritchard, adopts the same system of grouping, 

 adding to those above named two other genera, Hemiaulus, and Hy- 

 drosera, but gives more distinct characteristics than the former author. 

 His diagnosis rests mainly on the convexity of the frustules, in con- 

 sequence of which the lateral valves " enter largely into the front 

 \'iew," and on the development of processes on the valves. Grunow 

 adopts the group with no more distinct definition than the following. 

 "Side view longish, or having three, four, or more angles," and in- 

 cludes in it four genera, namely, Isthmia, Biddulphia, Amphitetras,and 

 Triceratium. Heiberg marks the group by the fact of the processes 

 springing from the valve obliquely outwards, and places under it the 

 genera Cerataulus, Biddulphia, Triceratium, Amphitetras'; and in a 

 sub-group named Biddulphiese cuneatse, the genus Eucampia also. 

 Immediately connected with the Biddulphiese, this Danish author 

 places another group, the Hemiaulidae, mainly distinguished from the 

 former by this one feature, that the processes, instead of springing 

 from the valve obliquely, are placed at right angles with the plane of 

 the base. 



The genus Isthmia which Klitzing, Ealfs, and Grunow include in 

 the Biddulphiese, differs considerably in these respects, that the frus- 

 tules on the front view are not symmetrical, and the valves are not 

 furnished with processes, the structure which Ealfs regarded as such 



