Unilocular foraminifera sculptured in reticular patterns are described. These have relatively short stratigraphic ranges within Argentine Upper Cretaceous and Tertiary sediments. Two types of lagenid forms are distinguished according to their apertural character: a) forms with an elongate and slender neck, generally associated with low energy environments, including Favolagena n. gen. (type species Lagena atilai Bertels) and b) forms with a heavy solid conus and a narrow duct connecting the aperture with the chamber lumen, a thicker wall and coarser surface sculpture. The latter forms are generally associated with shallow, high energy environments, and are herein included in Conolagena n. gen. (type species Conolagena argentina n. sp.). Among foraminifera a reticulate surface pattern occurs relatively frequently in the Cretaceous Nodosariacea and could be an important character in reconstructing the phylogeny of unilocular foraminifera. The following taxa are described as new: Favolagena ardolinoi, Conolagena argentina, C. tetratransversa and Conolagena? mateformis. INTRODUCTION The unilocular foraminifera have been infrequently studied until the last decade, when they have been considered both in monographic catalogs (Boltovskoy and Watanabe 1977; Boltovskoy and Giussani de Kahn 1982, 1983; McCulloch 1977; Popescu 1983; Malumian and Carames 1989) and from a revisional systematic point of view (Jones 1984; Patterson and Richardson 1987, 1988). The general opinion has been that they are of little value in applied stratigraphy or paleoecology mostly due to their low abundance relative to multilocular foraminifera. This attitude prevails despite the diversification of the unilocular forms during the middle Eocene in deep (Boltovskoy and Giussani de Kahn 1983) and shallow environments (Malumian and Carames 1989), which produced almost as many species as those of multilocular foraminifera. Malumian and Carames (1989), in a study of non-reticulate unilocular foraminifera from southern South America, found that despite their relative scarcity, the unilocular foraminifera can be used to differentiate Tertiary assemblages. Forms with reticular sculpture in particular have restricted distributions, and much of their apparent long chronological range is due to extreme lumping. That lumping reached the point where nearly all unilocular forms that exhibit some type of hexagonal pattern, from the Upper Cretaceous to Recent, were included in Oolina hexagona (Williamson). Not one of the fossil unilocular taxa revised by Malumiain and Carames (1989) in southern South America is referable to Williamson's species. THE RETICULAR ORNAMENTATION As in other shelled invertebrates (cf. Seilacher 1985), the definite and truly reticulate pattern is a rather rare sculpture among multilocular foraminifera. As far as is known by the authors, only six benthic species (Malumian 1990a), ranging from Jurassic to Albian and restricted to the Nodosariacea, have a true reticular surface: Marginulina pristipellis Ludbrook, Astacolus microdictyotos Espitalie and Sigal, Cristellaria dictyodes Deeke, Flabellina tenuistriata Franke, Cristellaria (Astacolus) micropunctata Fretzen, Marginulina rete Espitalie and Sigal. Reticulate sculpture is thus absent from the Cenomanian to Campanian. During the Campanian appeared the reticulate form Neoflabellina and in Australia the first known monolocular species, ascribed to Lagena hexagona (cf. Belford 1960). Lagena hexagona apertura Balakhmatova, from the Maastrichtian of the West Siberian Lowland, is the oldest reticulate unilocular species described from the Cretaceous. In Argentina, there is an exceptional abundance of unilocular reticulate forms in the marginal marine Maastrichtian shales of the Jagtiel Formation. Nearly 60 Tertiary to Recent unilocular reticulate species have been described, whereas very few multilocular foraminifera of this age show reticular ornamentation. Among the Buliminacea they are relatively common in the genera Bulimina and Bolivina; among others: Bulimina peanuta Boltovskoy and Giussani de Kahn, B. schischkinskye Samoilova, B. marksi Drooger, B. orphanensi Berggren and Aubert; and several bolivinids: Bolivina compacta Sidebottom, B. merencuanai Sellier de Civrieux, B. pseudoplicata Heron-Allen and Earland, B. torqueata Cushman and McCulloch, B. variabilis (Williamson), B. lowmani Phleger and Parker. On the other hand, in the Cassidulinacea the genus Favocassidulina, restricted to the Pacific Ocean, has a coarse, honeycomb-like ornamentation. And also the reticular ornamentation is restricted to a very few miliolids, such as Spiroloculina foveolata Cushman, Rupertianella rupertiana (Brady) and Quinqueloculina variolata d'Orbigny, the latter including Q. antillarum, Triloculina carinata, T. bicarinata and T. reticulata as synonyms (cf. Le Calvez 1977). Surface ornament has been shown to be subject to phenotypic as well as genotypic influence and is therefore considered to be of restricted use for taxonomy (cf. Hermelin and Malmgren 1980). Surface ornament seems to evolve independently in a number of unrelated benthic and planktonic, i.e. Favusella washitensis (Carsey), foraminiferal groups at different times. micropaleontology, vol. 37, no. 4, pp. 393-406, pls. 1-3, text-figures 1-3, 1991 393 This content downloaded from 157.55.39.123 on Mon, 18 Jul 2016 05:46:25 UTC All use subject to http://about.jstor.org/terms N. Malumidn, C. Niiez and A. Carames: Unilocularforaminifera of reticular surface from Argentina TEXT-FIGURE 1 Map localities.