Late Miocene Ostracoda from NW Libya

Nine ostracod species from the Late Miocene Al Khums Formation (exposed 2 km north of Qabilat ash Shurfah, NW Libya) are described and illustrated in this paper. Of these, four species, namely Cytherella libyaensis, Actinocythereis spinosa, Keijella africana and Neomonoceratina miocaenica, are new; one was established by Doruk (1980), one by Moyes (1965) and the other three species are left under open nomenclature. These species support the macrofossil, foraminiferal and other ostracod (Innocenti & Pertusati, 1984 and El-Waer, in press) evidence in suggesting a Late Miocene age.

. The study area. with greatest height at the posterior margin. Dorsal margin straight, sloping gently to the anterior margin. Ventral margin slightly concave in the middle and curved upwards anteriorly. Posterior margin is rounded. The lateral surface is covered by coarse pits. The area of the muscle scar attachment is indicated by a small, shallow depression. The left valve is larger than the right. Sexual dimorphism is pronounced, the presumed males are more elongate and less high than the females. The internal features not visible. ( El-Waer (in press), but the latter species differs in having a less arched dorsal margin and a more pointed posterior end than the present one. This species is represented only by closed carapaces and it has not been possible to ascertain the finer morphological details. It is placed in Propontocypris on the basis of the general shape. Occurrence. 2 km north of Qabilat ash Shurfah, Late Miocene, sample 3.

Superfamily Cytheracea Baird, 1850
Family Leptocytheridae Hanai, 1957 Genus Callistocythere Ruggieri, 1953 Callistocythere sp.  holotype. male carapace from right. HL.i.317.T. 1 0 ( x 68). HU.317.T.5 ( x 75). is a strong straight, horizontal median ridge which ends about one-fifth length from the posterior end. A strong ridge runs from the eye tubercle parallel to the anterior margin and about midway between the anterior and the sub-central tubercle. This rib curves round into an irregular ventral-lateral rib which ends in a rhombic tubercle again ends almost one-fifth length from the posterior marginal thickening, a rather irregular rib which runs near the anterior and roughly parallel to it and an oblique rib parallel to the posterodorsal margin and midway between that margin and the posterior termination of the median rib. The ornamentation is completed by a series of transverse ribs and intervening fossae of variable shape and size.

El-Waer
Dimensions of figured specimen (in pm) . consists of a combination of small nodes and fine denticles which continues along the ventral margin. The posterior margin is subtriangular, slightly pointed in the middle and decorated with small spines. The lateral surface is covered by strong blunt spines and by reticulation in the area behind the anterior margin and in the muscle scar area. Fine nodes occur scattered over the surface, some of them tending to form a longitudin-al row over the ventral margin. Eye tubercle is very marked. The muscle scar pattern is clear and consists of vertical row of four adductor scars with U-shaped frontal scar in a pit. The hinge is typical of the genus. Sexual dimorphism was not observed.

Dimensions of figured specimens (in pm) .
Holotype, left valve, HU.317.T.7. 830 384 Paratype, left valve, HU.317.T.8. 825 380 Remarks. This new species of Actinocythereis compares closely with Actinocythereis libyuensis El-Waer (in press). A . spinosa differs in having strong blunt spines on the lateral surface and the area behind the anterior margin covered by reticulations. In addition, it has some similarities to Actinocythereis ramuniuensis Khosla & Pant (1981), but the latter species differs in lacking ventral marginal spines and is not reticulate in the area behind the anterior margin. Occurrence. Only at the type locality: sample 3 of the section 2 km north of Qabilat ash Shurfah.

Length Height
Genus Keijella Ruggieri, 1967 Keijella africana sp. nov. Remarks. The present species has some similarities to Keijella hodgii (Brady, 1866) as figured by Ruggieri (1967), Doruk (1973) and El-Waer (in press), but the latter differs in that the anterior series of pits run in a single line just behind the anterior margin and the males are less high. K . africana is also somewhat similar to Keijella clauda Doruk, 1973, but the latter differs in lacking the pits on the lateral surface and the sloping dorsal margin. Occurrence. In samples l b , 2 and 3 of the section 2 km north of Qabilat ash Shurfah.
Genus Carinovalva Sissingh, 1973 Carinovalva carinata (Moyes, 1965) (PI. 1, fig. 12 Description. Carapace subrectangular to subrhomboidal in lateral view, with greatest height at the anterior r cardinal angle. Anterior margin broadly and obliquely rounded. Ventral margin fairly straight, slightly convex in the middle, curving upwards posteriorly. Lateral surface with a vertical sulcus which is widest dorsally and dies out above the ventral lateral ridge. The lateral surface is characterised by ridges. The ventrolateral ridge runs parallel to the ventral margin, is slightly alate posteriorly and joins the ventral rib anteriorly. The posterodorsal ridge commences behind the sulcus at above one-third height below the dorsal margin, curves upwards posterodorsally and ends behind the posterior cardinal angle. The median ridge starts from the middle of the ridge parallel to the anterior margin, runs across the median sulcus, and continues to join the inner posterodorsal rib posteriorly. The ventral rib originates from the anterior end of the median ridge, curves down parallel to the ventral margin to the posteroventral corner where it runs into the posterior rib. A small eye tubercle is present. The muscle scar pattern and the hinge are typical of the genus. Sexual dimorphism is marked, the presumed males being more elongate and narrower than the females.

Dimensions of figured specimens (in pm)
. Material. Five carapaces. Description. Carapace elongate to subovate in lateral view with greatest height at one-third the length. Anterior margin obliquely rounded, posterior margin more narrowly slightly rounded. Dorsal margin nearly straight, sloping gently backwards posteriorly. Ventral margin straight, curved upwards posteriorly. The lateral surface is finely pitted, the pits being arranged in a Length Height concentric pattern around the margins. Sexual dimorphism present, the presumed males being more elongate than the females. N o internal details were seen as no single valves were obtained.  Oertli (1956) and El-Waer (in press); the latter differs in having the ventral margin slightly concave in the middle and narrower posterior end. Occurrence. 2 km north of Qabilat ash Shurfah, Late Miocene, sample 3.