CYTHERIDEIS ACUMINATA. 43 



This species is named after Mr. C. Davies Sherborn, F.G.S., who has kindly 

 given us great help in the preparation of this Supplemental Monograph. 

 Localities. — Chalk, Horstead, and Mill Bay, Island Magee, co. Antrim. 



VI. Cytheeideis, Jones, 1857. 



Restricted and defined by G. S. Brady and A. M. Norman, ' Trans. Roy. Soc. 

 Dublin,' ser. 2, vol. iv, 1889, p. 226. " Shell slender, elongate, subovate, tapering 

 and depressed towards the front, not much compressed laterally. Hinge-margins 

 nearly simple; shell smooth, finely punctate; right valve overlapping the left in 

 the centre of the ventral surface." (The limbs are then described.) 



1. Cythbrideis paeallbla, sp. nov. Plate IV, figs. 5 and 6 (figured upside-down). 



Length '83 ; height "33 ; thickness '16 mm. 



A unique valve of a small subcylindrical carapace. If the figure be looked at in 

 the reversed position it is narrow-oblong, compressed and rounded at one (anterior) 

 end, and obliquely subacute at the other ; edge view (of the united valves) narrow- 

 lanceolate, or compressed ovate, sharp anteriorly and blunt behind ; surface 

 smooth. 



This may be a Gytherideis, although the anterior is more fully rounded than the 

 posterior end. Excepting that the posterior end in this case is obliquely truncate, 

 there are some comparable recent forms, such as Cytherideis cylindrica, Brady, ' Les 

 Fonds de la Mer,' vol. i, part 1, livr. 8, 1869, p. 113, pi. xiii, figs. 11 and 12 ; and 

 G. Imvata, Brady, ' Challenger Report,' 1880, p. 146, pi. vi, figs. 5 a — d ; also a 

 Tertiary species (from the Antwerp Crag),' (7. recta, Brady, ' Trans. Zool. Soc.,' vol. 

 X, 1878, p. 406, pi. Ixiii, figs. 3 a — d.. In some respects C. Igevata is nearest in 

 shape, but there is so much difference that we give our Irish specimen a separate 

 name, C. parallela. 



Locality. — Chalk, Keady Hill, co. Londonderry. Collected from the dust of a 

 chalk-flint, by Mr. Joseph Wright, F.G.S. 



2. Cytherideis acuminata (Alth). Plate IV, figs. 40, 41 (figured upside-down). 



Cttheeina acuminata, Alth. Keuss, in Haidinger's Nat. Abhandl., vol. iv, pt. 1, 



1851, p. 49, pi. vi, fig. 8 (not 7), dravrii upside- 

 down. 



Cttheee? "Wbightii, Jones, MS. Systematic Lists, &c., Belfast Nat. Field Club, 



vol. i, Appendix iii, 1875, p. 81. 



