PONTOCYPRIS TRIGONALIS. 3 



CO. Antrim ; and similar specimens at a quarry half-a-mile north of the railway- 

 terminus at Larne, co. Antrim, and at Keady Hill, co. Londonderry. 



PL II, fig. 51, and PI. Ill, figs 33 and 34, were collected by Dr. G. J. Hinde, 

 F.G.S.,^ from the Glialh of Horstead, Norfolk. 



II. PoNTOCTPEis, 0. 0. Sars, 1865. 



Valves " higher in front than behind, elongated, and subreniform or sub- 

 triangular," G. S. Brady, 'Trans. Zool. Soc.,' vol. x, 1878, p. 381. 



1. PoNTOCTPRis TRIGONALIS, sp. uov. Plate III, figs. 25 and 26 ; and Plate IV, 



figs. 1 and 2. 



Fig. 25 and fig. 1. Length '55; height '25; thickness '2 mm. 



Valve subtriangular, rounded in front, acute behind, straight below (on the 

 ventral margin), obliquely arched above, sloping away backwards from the antero- 

 dorsal border where the arching is highest at the anterior third.^ Edge view 

 of the carapace long, compressed-oval ; end view sub-oval. 



There are some known forms from the Cretaceous strata of Europe which are 

 closely related to our P. trigonalis, but the English specimens are much more 

 symmetrically rounded on the anterior and straighter along the ventral margin 

 than the figured Cretaceous forms, such as Cytherina acuminata, Alth, Haidinger's 

 *Naturw. Abhandl.,' vol. iii, 2 Abth., 1850, p. 198, pi. x, fig. 16 — a bad figure, 

 but referred to by Reuss under the same name, op. cit., vol. iv, 1 Abth., 1850, 

 p. 33, pi. vi, figs. 7 and 8 (not alike) ; C. aMenuata, Reuss, 'Bohm. Kreideform.,' 

 vol. ii, 1846, p. 104, pi. xxiv, fig. 15, refigured as Bairdia attenuata, Reuss, 

 'Denksch. Akad. Wien,' vol. vii, 1854, p. 140, pi. xxvi, fig. 3 ; also Cytherina 

 laevigata, Romer, ' ISTordd. Kreideg.,' 1841, p. 104, pi. xvi, fig. 20, refigured as 

 Gytherideis Isevigata by Reuss, in Geinitz's ' Elbthalgeb., &c.,' pt. 2, 1874, p. 150, 

 pi. xxviii, figs. 1 — 3. These three are not alike, but possibly comprise one female 

 and two male individuals ; fig. 2 is somewhat like the male of P. faha (Reuss) as 

 figured by G. S. Brady ; see above, p. 2. There are also some Tertiary forms 

 described and figured by Dr. A. E. von Reuss in Haidinger's ' Naturw. Abhandl.,' 

 vol. iii, 1 Abth., 1850, as Cytherina lucida and mytiloides, that seem to belong to 



1 See his memoir on the ' Fossil Sponge-spicules from the Upper Chalk found in the Interior of 

 a single Flint-stone from Horstead, Norfolk,' 8vo., Munich, 1880. 



2 The drawing, fig. 25, does not make it suiEciently convex here, and fig. 26 is wrong in giving 

 a double straight line at the junction of the valves. 



