On some Brachiopods from the Ordovician of Preservation Inlet, New Zealand.
[Read before the Otago Institute, 12th September, 1933; received by the Editor 30th September, 1933; issued separately, September, 1934.]
A Small collection of minute oboloid brachiopods has been submitted to me for determination by Prof. W. N. Benson. The fossils occur on two small slabs of black slate, in groups of three separate valves. The surfaces of the slabs are counterparts of one another.
On all of the valves the concentric ornament is shown, so that it is most likely that they represent the corresponding valves of each of the three specimens.
These minute fossils may be regarded as belonging to the atrematous obolid form, Leptobolus, having a terminal foramen, thin shell, and feeble divergent septa, of which traces only are seen in one or other of the specimens.
In addition to the form above mentioned there is another, badly preserved, brachiopod, tentatively referred to cf. Obolus sp., but practically a cast. It is associated on the same slab with Bryograptus consobrinus.
Description of Specimens.
Genus Leptobolus, James Hall
Leptobolus Novaezelandiae, sp. nov.
Plate 11. Figs. 1, 2, 3, 4.
Description of Syntypes.—Valves on opposite faces of slabs (marked 2A and 2B). Shell substance thin, corneous and glistening. Valves roundly ovate, with the apical region slightly prominent and subacute. Anterior margin widely rounded; cardinal or posterior margin flattened on either side of the foramen, which is conspicuous.
Shell-surface ornamented with closely set, wavy growth-lines, about 20 in the space of a millimetre. These growth-lines are somewhat tegulate or over-lapping. The shell-surface also shows traces of excessively fine radii, whilst the anterior margin shows radial
fracture lines due to excessive crushing. Figs. 1 and 2 appear to represent the pedicle valve, whilst figs. 3 and 4 are probably of the dorsal valve, with divergent furrows.
Dimensions.—Length, 3 mm.; width, 3.2 mm.
Observations.—Several related species of this genus may be compared with the present form. Leptobolus insignis, J. Hall (1872, p. 227, pl. vii, fig. 17), from the Utica Slate, shows a similar roundly ovate outline, and, moreover, is finely striate. It differs, however, in not having undulate growth-lines. The present writer has also described a species of Leptobolus from Heathcote (Middle Cambrian) as L. truncata (Chapman, 1917, p. 93, pl. vi, figs. 3, 3a), but this differs in the trigonal outline of the valves.
Locality.—Nos. 2A, 2B, Loc. 26. Morning Star Mine, Preservation Inlet, N.Z.
Horizon.—Top of L 3 or lower part L 2.
Genus Obolus Eichwald.
cf. Obolus sp.
Plate 11. Fig. 5.
Observations.—The specimen provisionally referred to this genus has evidently been crushed. It represents a decorticated transversely ovate valve, probably dorsal, and shows the divergent furrows of an obolid, whilst there are traces on the anterior margin of widely spaced furrows.
Dimensions.—Length of valve, 3.66 mm.; width, 5 mm.
Locality.—No. 770, Loc. 19. Preservation Inlet, N.Z.
Horizon.—From about the same horizon as the foregoing slab with Leptobolus novaezealandiae, viz., top of L 3 or lower part of L 2, associated with Bryograptus consobrinus. The Lancefieldian horizons are given in a reversed sequence to deposition, following T. S. Hall in his early work.
Explanation of Plate.
Fig. 1. Leptobolus novaezelandiae, sp. nov. No. 2A. Loc. 26. Morning Star Mine, Preservation Inlet, New Zealand. Pedicle valve. Syntype. X 17.
Fig. 2. Ditto. Sketch showing salient characters. X 4.
Fig. 3. L. novaezelandiae, sp. nov. No. 2B. Loc. 26. Morning Star Mine, Preservation Inlet, New Zealand. Dorsal valve. Syntype. X 17.
Fig. 4. Ditto. Sketch showing salient characters. X 4.
Fig. 5. cf. Obolus sp. No. 770. Loc. 19, near to that of above species. Cast of dorsal valve (badly preserved). X 3.
Chapman, F. 1917. The Heathcote Fauna. Rec. Geol. Surv. Vict., Vol. iv, Pt. 1, pp. 89–102, pls. vi-vii.
Hall, James. 1872. Twenty-fourth Report N.Y. State Mus. Nat. Hist.
Fig. 1.—Leptobolus novaezelandiae, sp. nov No. 2A. Loc. 26. Morning Star Mine. Preservation Inlet, New Zealand. Pedicle valve. Syutype. X 17.
Fig. 2.—Ditto. Sketch showing salient characters. X 4.
Fig. 3.—L. novaezelandiae, sp. nov. No. 2B. Loc. 26. Morning Star Mine, Preservation Inlet, New Zealand. Dorsal valve. Syntype X 17.
Fig. 4—Ditto. Sketch showing salient characters. X 4.
Fig. 5.—cf. Obolus sp. No. 770. Loc. 19. near to that of above species. Cast of dorsal valve (badly preserved). X 3.