Page:Quarterly Journal of the Geological Society of London, vol. 28.djvu/223

 during floods along with the muddy deposits, and so spread out along a shore. They certainly appear as if broken up; for none of the fibres appear perfect.

8. The beds of the Menevian group now come in, at first gritty and of a grey colour, and rather unfossilferous, then becoming darker in colour and of a finer grain, and at last almost a fine black slate. Most of these beds must have been deposited in deep water, as they are not accompanied by sandstones until the very last, near their junction with the Lingula-flags. In the finer beds fossils are very plentiful, and there is also a corresponding increase in the variety of forms.

9. The true Lingula-flags, a series of sandstones and shales, occasionally ripple-marked. Very barren for the most part, and showing a return to shore-deposits.

These successive changes, producing such varied conditions of deposit, must have had much to do with causing barrenness in parts of the strata, and with the appearance, on the other hand, of successive zones of animal life. The continuation of the same genera through a great thickness of shore or shallow-water deposits, as is the case in the Longmynd and Lingula-flags, and the rapid dying out and shorter range of the genera in finer beds or deep-sea deposits, like the bulk of the Menevian group, are interesting facts, and deserving of consideration when we seek for natural laws to account for the conditions presented to us at these early periods.

Note on the Entomostraca from the Cambrian Rocks of St. David's. By Prof. T. Rupert Jones, F.G.S.

1. Leperditia Hicksii, Jones. Pl. V. fig. 16 (reversed and imperfect).

Small, ovate ; hinge-line short ; posterior margin broadly curved, anteriorly rather narrower. Ocular spot indicated by a subovate, smooth, and faintly depressed area, reaching up to the hinge-line. Muscle-spot marked (on one side) by a faint irregular subcentral depression, whence a branching vein-like line of bright pyrites runs downwards nearly to the ventral border. Surface mostly punctate by the exposed cellular structure of the test, which has been converted into iron-pyrites, and nearly bared of its outermost layer.

This is the smallest Leperditia I know, and differs from others chiefly in its very nearly oval outline, and in the relative largeness of its eye-spot.

The still smaller Primitia solvensis was at first classed as a Leperditia, but has been subsequently referred to a more appropriate genus.

The above-described old Cambrian Leperditia is here named after its discoverer.

2. Entomis buprestis. pl. V. fig. 15.

Leperditia bupestris, Salter, Brit. Assoc. Rep. 1865, Trans. Sect. p. 285.

L. punctatissima, Salter, Siluria, 1865, Appendix, p. 519.

This is nearest to Entomis divisa, Jones (Monthly Microsc.

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