Kaszab Zoltán (szerk.): A Magyar Természettudományi Múzeum évkönyve 72. (Budapest 1980)

Szabó, J.: Lower and Middle Jurassic Gastropods from the Bakony Mountains (Hungary). Part II.: Pleurotomariacea and Fissurellacea (Archaeogastropoda)

The riblets arise from the elements of a row of tubercles below the suture. The sharp riblets fade out at the selenizone. Similar riblets occur also on the band between the selenizone and the lower suture, but only on the younger whorls. These latter riblets become slight nodes on the last whorl, and appear rather as undulation of the longitudinal ornamental elements. Remarks — Despite of the characteristic shape and ornament, this form cannot be identified with any previously figured species of similar age. It resembles most closely the species "Pleurotomaria''' subreticulata of D'ORBIGNY. This latter, however, shows small, denser and weaker ribs at the place of the tubercle-row of our specimens. D'ORBIGNY'S form has an elevated, keel-like selenizone, while the here described form shows angulation on the whorl-surface. The spire angle and the dimensions are similar in both forms. Distribution — Bakony Mts., Kericser: beds with mixed Obtusum to Ibex Zone fauna. Bathrotomaria mandokii sp. n. (Plate II: figs. 2, 3, 4) Holotypus : Plate II: fig. 3. — Locus typicus: Bakony Mts., Bakonybél, Somhegy. — Stratum typicum: Limestone infilling a horizontal submarine fissure.

— Derivatio nominis: After the name of L. Mándoki, a student in geology, who collected the type specimen. — Diagno sis Selenizone is not elevated, and only its adapical half is situated upon the angulation of the whorl surface of the adult shell; ramp is ornamented with spiral grooves; base hardly convex. Measurements: H HL HA W D A Plate II: figs. 2-3 28 16 10 26 69° Plate II: fig. 4 14 9 11 72° Material — Five fragmentary specimens well complementing one another, and having shell with a single exception. Shape — Dextral form of average size, with gradate spire. The whorl-surface is angular. A hardly convex, broad ramp runs below the suture, and below the angulation appears a flat band, which is subparallel to the axis. The selenizone is wide, running slightly below the angulation in the juvenile whorls, then partly on the angulation. The selenizone is somewhat concave, later becoming convex. The surface of the whorls curves with a rounded periphery into the hardly convex base. The periphery shows a weak longitudinal swelling occasionally. The umbilicus is moderately open. The umbilical margin is rounded-angular, the peristome is pentagonal. An internal mould shows the impression of the slit, which is of c. 40° in length of arch. Ornament — The whole whorl-surface, as well as the base, is covered by spiral ornament. The juvenile spiral threads fade out on the ramp of the later whorls, leaving only rare grooves as longitudinal elements. The growth-lines and the transverse threads are prosocline on the ramp, slightly opisthocline below the selenizone, and opisthocline, forming weak and reversed "S"-lines on the base. Embryonal shape and ornamen t

—The protoconch and the first whorl are slightly depressed, the adult coiling can be seen from the second whorl onwards. The concave selenizone appears firstly about a half whorl after the protoconch. After an other half whorl, the initially rounded surface becomes angular. The selenizone courses below the angulation, even on the juvenile shell, removing onto the angulation as late as about the fourth whorl. The selenizone becomes convex simultaneously, with a flat transitory portion. The ornament, appearing together with the selenizone, is cancellate. Except the appearance of the selenizone, there is no sharp boundary between the embryonal and the juvenile shell. Remarks — The dimensions are close to those in B. reticulata (Sow., 1818), but the ramp is narrower, steeper and more convex. On the other hand, the selenizone is not elevated, broader, and only its adapical half falls upon the angulation of the whorl-surface. In B. reticulata the elevated selenizone coincides with the angulation, and the longitudinal ornament consists of spiral cords throughout on the shell, while the here described form shows corresponding widely spaced grooves on the ramp after the juvenile shell. Distribution — Bakony Mts., Somhegy: Humphriesianum to Garantiana Zones.