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)

Ornament — The whole whorl-surface and the base is ornamented with spiral cords. These are nearly equal in strength, becoming weaker only with the flattening of the peripheral swollen band below the selenizone. The transverse ornament results from the growth-lines and the parallel costellae, the strength and density of which are equal to those of the spiral cords. The costellae tend to become slightly stronger toward the suture. The longitudinal and transverse ornament show a cancellate general sculpture. On the base the spiral cords are intersected only by the growth-lines. These latter are prosocline, somewhat prosocryt above the selenizone, opisthocryt between the selenizone and the periphery, then opisthocline with the flattening of the longitudinal swollen band, and prosocyrt on the base. Remarks — This form is similar to P. periferialis sp. n. in the small spire angle, and in the possibly similar habit of the shell. P. niobe (D'ORB., 1854) resembles the juvenile shell, but it has markedly higher whorls and selenizone higher on the whorls. On the basis of the differences in the shape and the tuberculate periphery, the similarly acutely spired P. strobilus (DESL., 1849), certain P. conoidea (DESH., 1831), as well as P. culminata (HEB.

—DESL., 1860) can be easily distinguished. Distribution — Bakony Mts., Somhegy, condensed Humphriesianum to Garantiana Zones fauna. Pyrgotrochus sp. (Plate III: fig. 8) 1861 : Pleurotomaria princeps KOCH et DUNKER — STOLICZKA, p. 189, pi. 4, fig. 8. Material— Two poorly preserved specimens. Shape — Dextral form with broad, flattened base. The whorls are markedly flattened axially,. with sigmoidal surface. The selenizone courses on the abapical half of the whorls. The umbilicus is wide, open. Ornament — The shell is ornamented with spiral cords, growth-lines and rows of tuberclesabove and below the suture. Remarks — The specimens can be identified with the figure of Stoliczka mentioned in the synonymy, but his measurements need revision, and suggest possibly a new species. However, theavailable restricted material unables to prove this fact. Distribution — Bakony Mts., Kericser, beds with mixed Obtusum to Ibex Zone fauna. Pyrgotrochus? problematicus sp. n. (Plate IV: figs. 1-3) Holotypus : Plate IV: fig. 1. — Locus typicus: Bakonybél, Somhegy. — Stratum typicum: Limestone infilling of a horizontal submarine fissure. — Derivatio nominis: referring to the uncertainties of uniting this form with the known genera. — Diagnosis : Conical form with shell consisting of numerous whorls. Surface of the whorls slightly convex, angular in the level of the selenizone situating at the lower third of whorls, periphery slightly swollen. Measurements: H HL HA W D A Plate: IV. fig. 1 55 27 16.5 22 47 49° Material— It is one of the most common forms in the Bajocian gastropod fauna of Somhegy. Owing to the exceptionally thin shell, all the 16 available specimens are damaged, however the fragments can be well complemented with one another. Shape — Dextral form with high, conical shell. The outline of the spire is slightly cyrtoconoid near the apex. The whorl-surface is convex, somewhat angular, with the wide, convex selenizone coursing on the abapical half of the whorl. The place of the selenizone marks the most elevated part of the whorl-surface. The surface runs slightly concavely below the selenizone, then continues in an other, somewhat convex portion, lower slope of which evenly rounds into the base. The base is flattened, with wide, open umbilicus. The base rounds with a wide arch into the umbilicus, without angulation. The peristome is unknown. Ornament— The juvenile whorls are covered by spiral threads and similarly stengthened threads being parallel to the growth-lines. The transverse threads disappear on the later whorls, and here the ornament consists of only the spiral elements and the growth-lines. The spiral ornamental elements are spiral threads on and below the selenizone and on the base. Above the selenizone, widelyspaced spiral grooves are visible, spiral threads confining to a single band below the suture. On the