Pleurotomaria sp. 1

Pleurotomaria sp. 1

( Figs 85–90 View Figs 85–96 )

Material – Single, fragmentary specimen (GBA 2018/002/0007), consisting of partly preserved last two whorls, and base .

Measurements – Height of the specimen: 12.7 mm.

Description – The remains belong to a species, having rather low shell consisting of about 6 whorls that form a feebly gradate, conoidal outline. The available whorls have a spiral angulation, which abaxially limit a narrow, rather steep, flat ramp above a wide outer face, which slopes just a little more than the ramp. The adapical part of the outer face is concave and actually this belt distinguishes the ramp. At about the middle of the outer face, the convex selenizone can be found. A shallow and narrow concave belt separates it from the slightly swollen, lowermost belt that turns into the concave base through a rounded angulation. The wall of the base is slightly convex but in adaxial-adapically oblique position; most probably, the shell is narrowly phaneromphalous.

The ramp is densely covered by club-like, collabral riblets, their nodes are along the angulation of the whorls. In similar density, the peripheral swollen belt is sculptured with prosocline-prosocyrt riblets, which extend also to the outermost belt of the base. In a narrow abaxial belt of the ramp and in the whole swollen zone of the outer face, spiral threads cross the riblets. Two spiral threads are also immediately below the angulation. The selenizone is edged by two spiral threads and a spiral cord runs in its midline, crossed by dense, thin lunulae. Spiral threads ornament also the base. The growth lines are slightly prosocline on the ramp, strongly prosocline and feebly prosocyrt between the angulation and the selenizone, prosocline and just visibly prosocyrt between the selenizone and the outer rim of the base. On the base, the growth lines are opisthocyrt, slightly prosocline in the abaxial two thirds belt.

Remarks – The habit of the ornament, especially on the ramp, is similar to those of the early teleoconch sculpture of P. nodulocostulata n. sp., P. wiesberghausensis n. sp. and P. nodulocincta n. sp. However, in the corresponding size of the shell, no other species has the riblets of the ramp and the peripheral zone in such density and shape as Pleurotomaria sp. 1 , profile of the whorls is also different. For the first glance, the remnants are also similar to Pleurotomaria tenuiclathrata by CLARK (1887) but it has wider and concave ramp, consequently clearly gradate outline, convex outer face with selenizone, ornamented by 3–4 spiral threads, and stronger and sparser ribs and nodes.

Distribution – Within Sinemurian to lowermost Pliensbachian (Lower Jurassic) part of the Hierlatz Limestone Formation in Hierlatz Alpe, Hallstatt, Austria.