44 



CARBONIFEROUS ENTOMOSTRACA. 



the Cypridinal notch on the sloping anterior margin under the projecting antero-dorsal 

 angle. The nearest approach to this structure among the species described in the 

 previous pages is seen in figs. 15 — 19, PI. II, Cypridina brevimenttim, and in figs. 30 

 and 31, PI. II, which we have doubtingly referred to Philomedes (p. 43). In both cases, 

 however, a large sinus and definite notch give a considerable gape to the closed valves. 

 In PoJycope, which is known to differ considerably from Cypridina in its organs, the 

 sinus is reduced to a minimum, and the notch is quite wanting, so that there is no gape 

 at all. The above-mentioned specimens, having still some amount of sinus, notch, and 

 gape, differ essentially from Polycope ; and they diff"er in degree, to a large extent, from 

 the above quoted Cypridinads. And as the features here referred to were doubtless in 

 strict relation with the capability and appliance of the internal organs and the extruded 

 swimming feet, we propose to group these few specimens under a new genus, Rhombina. 

 A marginal rim on the ventral edge of the valves may also be mentioned as a noticeable 

 feature, on account of its much greater development than in any other of the allied forms. 



There is some resemblance between Rhombina and certain forms of Aristozoe, one of 

 M. Barrande's Siluriaji genera from Bohemia, but the latter has usually antero-dorsal 

 tubercles and sometimes a nuchal sulcus. 



1. Rhombina Hibernica. Sp. nov. Plate II, figs. 32 a — c ; Plate V, figs. 13 a — c. 



Carapace subcylindrical, with slanting ends ; somewhat pod-shaped ; compressed 

 anteriorly. Carapace-valve almost a rhomb in outline, obliquely truncate at both extremi- 

 ties, with nearly parallel lines, but more acutely (60°) at the anterior end than at the 

 other (70°). The most prominent angle is at the antero-dorsal region, under which a 

 slight sinus notches each valve, making a small gape. 



The dorsal line is straight ; the lower margin is slightly convex, and is bordered by a 

 distinct raised rim. End-view of the carapace is acute-oval ; edge-view long compressed 

 ovate. 



Length \ ; height -g-; thickness ^ inch. Proportions 12 : 6 : 5. 



This species is represented by a well-preserved dark-coloured shell from the Carboni- 

 ferous Limestone of Little Island, Cork, and was brought to our notice by its 

 discoverer, Mr. J, Wright, P.G.S. 



[The figure 32 a, in PI. II, represents the valve upside down ; it is therefore refigured 

 in PI. V, fig. 13^?.] 



• 2. Rhombina Belgica. Sp. nov. Plate V, figs. 14 a — d. 



Carapace oblong-ovate, subcylindrical, truncated obliquely at the extremities, and some- 



