Clarella venusta ( Billings, 1872 )

Unger, Tanja, Hildenbrand, Anne, Stinnesbeck, Wolfgang & Austermann, Gregor, 2022, Biostratigraphy and taxonomy of polymerid trilobites of the Manuels River Formation (Drumian, middle Cambrian), Newfoundland, Canada, Geodiversitas 44 (33), pp. 1051-1087 : 1075

Clarella venusta ( Billings, 1872)

( Fig. 16 )

Anapolenus venustus Billings, 1872: 474-476 , fig.11;1874: 73, 74, fig.42.

Clarella venusta – Hutchinson 1962: 111, 112, pl. 17, figs 7-10. — Martin & Dean 1988: 19, pl. 1, fig. 13. — Whittington et al. 1997: figs 308.1a, b. — Fletcher 2006: pl. 34, fig. 11 (partim).

LECTOTYPE. — Specimen GSC No. 284a , Geological Survey of Canada, Ottawa, Canada, designated as lectotype by Whittington et al. (1997). From Chapel Arm, Trinity Bay , Newfoundland, Canada.

DIAGNOSIS. — Glabella not reaching anterior margin; L4 short; eye lobes from L1 to S4; pygidium with two pairs of short marginal spines.

MATERIAL EXAMINED. — Three cranidia of Clarella venusta ( NFM F-3069; NFM F-3548; NFM F-3657). All specimens range between 16.25 and 16.27 m ( Fig. 2 ) within the Manuels River Formation, type locality, Conception Bay South, Newfoundland, Canada .

OCCURRENCE. — Clarella venusta is rare in the middle Cambrian and only reported from southeastern Canada, eastern Newfoundland, in the Paradoxides hicksi and Paradoxides davidis zones ( Hutchinson 1962; Martin & Dean 1988; Fletcher 2006).

DESCRIPTION

The cranidium (NFM F-3096) is 22.2 mm in width and 15.8 mm in length. The width of the glabella is 10.3 mm and the length is 10.8 mm. Due to the preservation of NFM F-3548; NFM F-3657 a solid measurment was not possible. The three cranidia are preserved as one disarticulated internal cast and two moulds.

REMARKS

The cranidium of Clarella venusta is similar to Clarella impar ( Hicks, 1872) . The palpebral lobes of C. venusta are narrower and curved more sigmoidally than those of C. impar ( Cook, 1997) . The librigena illustrated by Fletcher (2006: pl. 34, fig. 12) is disarticulated and its suture of the librigena does not match that of C. venusta . It is here excluded from the species.

Figures

FIG. 16. — Clarella venusta (Billings, 1872): A, mould of a cranidium (NFM F-3096 from 16.25 m); B, disarticulated internal cast of a cranidium (NFM F-3548 from 16.25 m). Scale bar: 1 mm.

FIG. 2. — Lithology of the type locality of the Manuels River Formation, range chart of the here described species. Agnostid biozones from Hildenbrand et al. (2021) and polymerid biozones from Howell (1925).