Scurriopsis (Hennocquia) hettangiensis ( Terquem, 1855 )

Monari, Stefano, Valentini, Mara & Conti, Maria Alessandra, 2011, Earliest Jurassic patellogastropod, vetigastropod, and neritimorph gastropods from Luxembourg with considerations on the Triassic-Jurassic faunal turnover, Acta Palaeontologica Polonica 56 (2), pp. 349-384 : 355-357

Scurriopsis (Hennocquia) hettangiensis ( Terquem, 1855)

Fig. 5D–I .

?1844 Patella subquadrata sp. nov.; Dunker 1844: 188.

? 1847 Patella subquadrata Dunker ; Dunker 1847: 113, pl. 13: 18a, b.

?1850 Helcion dunkeri nom. nov.; Orbigny 1850: 215 (pro Patella subquadrata Dunker, 1844 non York, 1837).

1855 Patella hettangiensis sp. nov.; Terquem 1855: 281, pl. 18: 2, 2a.

1855 Patella dunkeri Dunker [sic]; Terquem 1855: 280, pl. 18: 3, 3a, 3b.

1866 Patella suttonensis sp. nov.; Tawney 1866: 88, pl. 4: 9a, b.

1884 Patella hettangiensis Terquem ; Quenstedt 1884: 755, pl. 215: 29.

1932 Scurria hettangiensis (Terquem) ; Haber 1932: 190–192.

1988 Scurriopsis dunkeri (Orbigny) ; Meier and Meiers 1988: 23, pl. 1: 1a, b.

1988 Scurriopsis (Hennocquia) hennocquii (Terquem) ; Meier and Meiers 1988: 23–24, pl. 1: 2a, b.

1988 Scurriopsis hettangiensis (Terquem) ; Meier and Meiers 1988: 24, pl. 1: 3a, b.

Material.— Thirty−three specimens: MNHNL BR 153, MNHNL BR 159, MNHNL BR 239, MNHNL BR 260, MNHNL BR 363, MNHNL BR 366, MNHNL BR 377, MNHNL BR 487, MNHNL BR 488, MNHNL BR 489, MNHNL BR 490, MNHNL BR 491, MNHNL BR 492, MNHNL BR 496, MNHNL BR 497, MNHNL BR 498, MNHNL BR 499, MNHNL BR 500, MNHNL BR 503, MNHNL BR 504, MNHNL BR 505, MNHNL BR 551, MNHNL BR 650, MNHNL BR 668, MNHNL BR 669, MNHNL BR 670, MNHNL BR 671, MNHNL BR 673, MNHNL BR 674, MNHNL BR 675, MNHNL BR 756, MNHNL BR 764, MNHNL BR 767, Brouch, Upper Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ). Three specimens: MNHNL HE 112, MNHNL HE 122, MNHNL HE 164, Brouch, Hettangian exact stratigraphical level unknown. Eight specimens: MNHNL GL154, MNHNL GL222 (four specimens), MNHNL GL250 (two specimens), MNHNL LI147, Luxembourg Sandstone Formation, locality and stratigraphical level unknown.

Dimensions.—See Table 1.

Description.—Medium−sized, limpet−shaped to cap−shaped shell with mamillated, moderately to strongly anterior apex. Shell wall somewhat thick. Peristome elliptical to subrectan−

doi:10.4202/app.2010.0098

gular and slightly narrower anteriorly. Width of peristome ranging 76–90% of its length. Height of the shell rather variable, 34–61% of its length. Posterior slope almost straight to definitely convex. Anterior slope slightly to strongly convex. Apex in anterior position at 56–73% of the total length of the shell. Surface of the shell covered with strong and sharp growth striae roughly forming threads. Obscure radial lines and riblets commonly present.

Remarks.—A comparison with Scurriopsis (Hennocquia) hennocquii Terquem, 1855 , type species of Scurriopsis (Hennocquia) Wenz, 1938 facilitates the subgenus attribution of the species described here. Scurriopsis (Hennocquia) hettangiensis ( Terquem, 1855) shows strong similarities with S. (H.) hennocquii in the elliptical shape of the peristome, which is narrower in the anterior part, and in the shape of the lateral profile. S. (H.) hennocquii is characterised by a thin, light radial ornament of the posterior slope which Wenz (1938) and Cox and Keen (1960) considered to be significant at supraspecific level. However, in S. (H.) hettangiensis the surface of the shell is frequently crossed by variably obscure radial lines occurring on the whole surface of the shell or only on some parts of it. The characters differentiating S. (H.) hennocquii from S. (H.) hettangiensis are interpreted here as distinctive only at specific level. In addition to the slightly more marked radial ornament and its exclusively posterior location, S. (H.) hennocquii differs from S. (H.) hettangiensis in having a narrower outline of the peristome and a lower profile with slightly concave anterior slope.

As pointed out by Terquem (1855), S. (H.) hettangiensis displays a high variability in the general shape of the shell. The shell is moderately to rather high. The slopes are slightly to strongly convex. In most of the specimens the apex is moderately anterior but in some specimens it shifts to a strongly anterior position during growth. The early juvenile shell is commonly rather high. During the juvenile growth the shape of the shell becomes more depressed. However, in some specimens the inflation of the shell increases again during the adult growth. Constant characters consist of a mamillated shape of the apical shell, and an elliptical−subrectangular, posteriorly larger outline of the peristomal edge. The growth striae are always well−marked and form a variably rough pattern of commarginal threads.

In the light of the strong variability described above, Patella suttonensis Tawney, 1866 is here synonymised with S. (H.) hettangiensis , as was suggested by Haber (1932). Patella dunkeri d’Orbigny, 1850 (= Patella subquadrata Dunker, 1844 , non York, 1837) is represented by very small specimens ( Dunker 1847: 113, pl. 13: 18) which could represent the juvenile stage of S. (H.) hettangiensis . In that case, the name of Orbigny’s (1850) species should have the priority ( Haber 1932). The poor information about P. dunkeri prevents more detailed comparisons. The shell ascribed by Terquem (1855) to P. dunkeri is strongly reminishent of some of the specimens described here. For this reason, it is here included in the synonymy of S. (H.) hettangiensis .

Helcion infraliasina de Ryckholt, 1852 ( Ryckholt 1852: 60, pl. 2: 26, 27; Chapuis and Dewalque 1853: 108, pl. 14: 6) from the Luxembourg Sandstone Formation differs from S. (H.) hettangiensis in having an evenly elliptical and less wide peristome, and in the surface of the shell which is ornamented with stronger radial striae.

Stratigraphic and geographic range.—Hettangian, Hettange−Grande (Lorraine, France); Late Hettangian ( Schlotheimia angulata Zone , Schlotheimia complanata Subzone ), Brouch ( Luxembourg); Late Hettangian to earliest Sinemurian, Sutton (South Wales, United Kingdom);?Early Hettangian ( Psiloceras planorbis Zone ), Halberstadt (Saxony−Anhalt, Germany).

Figures

Fig. 5. Patellogastropods from Brouch (Mersch, Grand−Duchy of Luxembourg), Late Hettangian (Schlotheimia angulata Zone, Schlotheimia complanata Subzone), Early Jurassic. A–C. Scurriopsis (Scurriopsis) schmidti (Dunker, 1844). A. MNHNL BR180, apical (A1) and lateral (A2) views. B. MNHNL BR109, apical (B1) and lateral (B2) views. C. MNHNL BR360, lateral (C1) and apical (C2) views. D–I. Scurriopsis (Hennocquia) hettangiensis (Terquem, 1855). D. MNHNL BR503, apical (D1) and lateral (D2) views. E. MNHNL BR260, apical (E1) and lateral (E2) views. F. MNHNL BR673, lateral (F1) and apical (F2) views. G. MNHNL BR363, apical (G1) and lateral (G2) views. H. MNHNL BR650, lateral (H1) and apical (H2) views. I. MNHNL BR497, lateral (I1) and apical (I2) views.