Eripleura, a new genus of ostracod from the Upper Jurassic of England and its relationship with Procytheropteron Ljubimova

A new genus of cytherurid ostracod, Eripleura, with the type species E. eleanorae sp. nov. from the Upper Oxfordian (? rosenkrantzi Zone) and Lower Kimmeridgian (baylei Zone) of southern England is described and compared with Procytheropteron. Two further species are described for the first time, Eripleura obliquicosta from the Lower Kimmeridgian cymodoce Zone, and Procytheropteron? elongatum from the Upper Oxfordian tenuiserratum Zone.


INTRODUCTION
In 1955, Ljubimova used the genus "Procytheropteron Mandelstam, 1955," but cited her own species, P. obesum, the genotype. Mandelstam's paper in which Procytheropteron was described as a new genus did not appear until 1956. In that paper, Cythere punctatula var. virginea Jones, 1849 was designated genotype. According to the International Code of Zoological Nomenclature, the actions of both authors were invalid; however, two points are pertinent to this discussion.
i. The name Procytheropteron must be accredited to Ljubimova and P. obesum stands as its genotype. The genus is ovate in outline, smooth to weakly reticulate, has marginal pore canals "present in great numbers at the anterior end" and a hemimerodont hinge.
ii. Mandelstam's concept of the new genus was not the same as Ljubimova's for C. punctatula virginea of Jones (1849) is a species of Neocythere Mertens (1956). In fact Morkhoven (1963, p. 258) considered Procytheropteron to be a junior synonym of Neocythere (Centrocythere) , a genus of Progonocytherinae with an amphidont hinge. In 1969, Kilenyi figured an elongate species from the baylei Zone of Dorset which he left in open nomenclature as Procytheropteron sp. 1. However, the species differs from Procytheropteron sensu Ljubimova in several respects, although it has a hemimerodont hinge. It is strongly costate, sulcate, elongate, has fewer anterior marginal pore canals and has a subalate ventral rib rather than the "sack-like" overhanging ventral margin as Ljubimova described. Species with these characteristics should be removed from Procytheropteron and Eripleura is here erected to accommodate them. A specimen more typical of Procytheropteron from the Upper Oxfordian Corallian Limestone of the Winter-borne Kingston Borehole is illustrated (Pl. 1, Figure  12) for comparison, although left in open nomenclature.
Several species from the British Oxfordian have been assigned to Procytheropteron on the basis of the hinge and the posteroventral inflation which partially interrupts the ventral margin. Procytheropteron? elongatum sp. nov. from the Upper Oxfordian tenuiserratum Zone of eastern England and Procytheropteron? pro-Zongatum (Sharopova) from the Lowerpanderi Zone of Russia (Sharapova, 1939;Fuller, 1980) are examples. The generic assignment is made only tentatively as they lack the numerous anterior marginal pore canals described by Ljubimova. are considerably more elongate and often show strong primary and secondary reticultion.  Marginal pore canals few (7-9 anteriorly and 3 posteriorly) straight and simple. Dimorphic. Remark. Eripleura shows some resemblance to Procytheropteron in terms of general outline and hingement. It differs, however, in its strongly costate ornament, including a subalate ventral rib, in the sulcus and in lacking the overhanging, "sack-like'' (Ljubimova, 1955) ventrolateral inflation. Internally, the marginal pore canals are fewer in number. Eocytheropteron differs in its hinge being crenulate throughout, the terminal elements merging imperceptibly with the median element. Procytheropteron subtrapezoides Bielecka, Blaszyk & Styk. 1976 Kilenyi (1978) confused the species with Eocytheropteron decoratum (Schmidt), a reticulate species of Cytheropterinae that lacks costae. The species is not common. It has been found in the ?rosenkrantzi Zone, Ringstead Waxy Clay of Ringstead Bay, Dorset (Whatley, MS 1965) and the baylei Zone of the basal Kimmeridge Clay in the stratotype area (Kilenyi, 1969). The present author has recovered the species from the regulare and rosenkrantzi Zones of the Ampthill Clay in the Nettleton Bottom Borehole, Lincolnshire [TF 1245 98231 (Wilkinson, 1983 Internally as for the genus. Hinge hemimerodont; marginal pore canals few, straight and simple; muscle scars consist of a vertical row of four oval adductors and a larger frontal scar. Dimorphic, the males being more elongate than the females.

SYSTEMATIC DESCRIPTIONS
Remarks. Eripleura obliquicostata sp. nov. differs from E. eleanorae in ornament, lacking the median rib complex, being distinctly reticulate and in having straight, subparallel dorsal and ventral margins. E. subtrapezoides (Bielecka, Blaszyk & Styk, 1976) differs in outline, in the position of the caudal process and in the ornamentation. The present species has been recorded from the Lower Kimmeridgian of the North Wootton Borehole, Norfolk [TF 6439 24571 and B.G.S. Borehole 81/41, east of Scarborough (California Sheet, 54" 22.197". , 0" 27.284'E.) (Wilkinson, 1983;Cox et al., in press