Original Description of Pietteia trispinigera by Szabo, 1983:
- "Large, bicarinate, dome-shaped embryonal shell; densely-ribbed juvenile whorls, followed by rare parabolic nodes on the angulation up to the penultimate whorl; three protrusion on the slightly expanded outer lip.
- Shape - The shell is dextral with high spire of slighly cyrtoconoid outline. The whorls are slighly convex with carinate middle part, and are bordered by sutures in moderately deep grooves. On the last whorl, below the periphery (i.e. the carina of the whorls), an other weak break is visible, and both continues into a protuding spine on the peristome. The base is convex on the upper part, and concave near the siphonal canal, without umbilicus. The peristome is markedly expanded, its upper part reaches to the carina of the penultimate whorl. The end of the spine in the continuation of the carina is slightly curved adaperturally and adapically. The lower spine is situated as somewhat arched from the bisector of the angle between the upper spine and the siphonal canal, in the direction of the latter. One unpreparable specimen shows a spine on the carina, ca. 240° before the last peristome. the other shells show only the scar of this element.
- Ornament - The whole teleoconch is ornamented by fine threads, which appear immediately after the end of the embryonal whorls. In the beginning these cover only the zone between the carina and the lower suture, but after about a half whorl cover the remaining part, too. These occur on the base also with the same density and strenght as on the whorls. Some lines are continued upon the peristomal protrusions. the transverse ornament is formed by opisthocyrt growth lines and ribs restricted to the juvenile shell. These latter ones run suture to suture for a lenght of about one whorl after the end of the protoconch, and are pointed on the carina. They become shorter gradually on the next whorls, resulting in nodes on the carina, rarer than the ribs. Most nodes are parabolic, showing by the growth lines clearly. The last ca. one and a half whorl lacks the nodes, but the strenght and run of the carina remains uneven.
- Embryonal shape and ornament - The axis of the protoconch coincides with that of the teleococnh, and is of dome-shape. Only trace of the nucleus is visible on the holotype: it is probably depressed and seems large. This is followed by three embryonal whorls visible by unaided eye, and these are separated from the teleoconch by sharp sculptural boundary. The somewhat convex whorls are smooth except the two tiny suprasutural carinae, only the last quarter-whorl bears gradually strengthening transverse threads. These become strong suddenly at the end of the protoconch, with simultaneous ending of the two tny carinae, and appearance of the mid-whorl carina characteristic to the teleoconch."
Remarks: According to the original description, the build-up of the outer lip in the genus Pietteia is characterized by a single spine beside the siphonal canal, in the place of the continuation of the periphery. The possession of two spines, recognized in this form, is a feature in the genus Dicroloma Gabb, 1868, but this is the only character differing from those of Pietteia. All the other features suggest this latter genus: i.e. the ribbed or tuberculate whorls, contrary the only spirally ornamented Dicroloma shell; the presence of only one, the upper marked carina and the representation of the lower as only a spiral cord in the last whorl of P. trispinigera sp. n., as in the congeneric forms, while the Dicroloma is bicarinate here.
Of the contemporary forms, P. hamus (Deslongchamps, 1842) is the most similar, but this has only two protrusions on the peristome, and is evenly ribbed up to the penultimate whorl, while P. trispinigera sp. n. is ribbed only in the juvenile shell, then nodose. P. tridactyla (Buvignier, 1843) bears similarly three peristomal protrusions, thus this is most similar in shape, in spite of the fact that these three rostra are markedly shorter. However, its ... equal ribbing is a clear distinguishing feature.
Etymology: tres (Lat.) = three; spine (Lat.) = thorn; gero (Lat.) = bears
Locus typicus: Bakonybél, Somhegy, Hungary
Stratum typicum: limestone infilling horizontal fissure, Bajocien, middle Jurassic
Measures: 30mm, diameter 18mm
- Szabo J., 1983, Lower and Middle Jurassic Gastropods from the Bakony Mountains (Hungary), Part. V. supplement to Archaeogastropoda; Caenogastropoda, Annales Historico-Naturales Musei Nationalis Hungarici, Tomus 75., Budapest, 1983, pp 27-46.