further back in past time, we find that our enquiry is greatly facilitated, not merely by reason of the reduction of our field of observation to a smaller accessible area of fossiliferous deposits, but also because the objects themselves become more and more reduced, not merely in numbers, but in diversity of forms, until at last we arrive at rocks in which the whole class is included in some two or three orders or families.

Thus in the rocks of Tertiary age Crabs (Decapoda-Brachyura) are apparently as abundant as in our recent seas.

But in the Secondary strata we perceive a visible diminution in the short-tailed forms, the earliest of which are, at present, only known in rocks of Oolitic age.

*

Lobsters (Decapoda-Macrura), however, are abundant in the Oolitic series, and extend back into primary or palæozoic times, the first being found in the Coal-measures.†

Through all these formations we find representatives of the principal living genera, with the exception only of those softbodied forms which could not be preserved in a fossil state, such as the "Brine-shrimp," Artemia salina; Cheirocephalus; and the parasitic Lerneonema, Argulus, Nicothoe, and other specialised forms.

As we scan the record of these old Carboniferous rocks, so rich in organic remains, we seem to stand on some lofty beacon-hill, whence we can cast our glance upwards and downwards along the stream of time. Beneath our feet lie buried the last representatives of those aboriginal races now quite extinct, the Trilobita and the Eurypterida, whose ancient hosts peopled the seas of Devonian and Silurian ages, and reached far away into the Cambrian epoch. Beside them lie the earliest representatives known of our modern Decapods, Stomapods, and Isopods, then but few and feeble, but now the dominant races of the Crustacean class.

Is this, then, the barrier-reef between the Palæozoic and Neozoic life-periods? Do we indeed find here the beginning of all modern forms of Crustacea, and the ending of all ancient ones? By no means; nor is there, as we have already observed, any period in the whole geological record at which a hard and fast line can be drawn dividing the class into recent and extinct families.

Certain groups, such as the Entomostraca, are represented throughout. Others, like the Amphipoda, may perhaps extend

Oldest known British Crab, Palæinachus longipes, H. Woodward, Forest Marble, Malmesbury, Wilts. See "Quart. Journ. Geol. Soc.,” 1866, Vol. XXII. p. 493.

† Anthrapalamon Grossarti, Salter, Coal Measures, Lanarkshire. "Quart. Journ. Geol. Soc.," 1861, Vol. XVII. p. 531.

See

*

into Silurian times; or, like the Isopoda, may reach back to the Devonian epoch.† The Cirripedia, a most aberrant group of Crustacea (represented abundantly in the seas of to-day by the pedunculated Lepas ("Ship Barnacle") and the sessile Balanus (or "Acorn Shell "), so common on the bottoms of ships which have been long at sea, and upon the piles of piers, and on seawalls, and rocks washed by the tide), carry back their history, the latter through the Tertiary rocks to the Upper Chalk, the former to the earliest Secondary rocks, whilst a single form is found in the Wenlock shale of Dudley (Upper Silurian).§

The King-Crabs, next to the Entomostraca, undoubtedly enjoy the most extended range in time; occurring in considerable numbers in the Lithographic stone of Solenhofen, with characters scarcely, if at all, differing from those species now found living on the east coast of North America and in the seas of China and Japan. About seven species occur in the Coal-measures (See Plate XC., figs. 6, 7, 8,), and one actually in the Silurian (See Plate XC., fig. 9) of Lesmahagow in Lanarkshire; these palæozoic forms closely resemble the larval stages of the living Limulus (See Plate XCI., figs. 21–24).

The accompanying Table will best exhibit the successive appearance of the chief orders of Crustacea, and beside them are placed the Arachnida, the Myriapoda, and the Insecta, with their representatives in palæozoic strata; thus giving the range of the entire sub-kingdom of the ARTHROPODA in time.

But omitting the solitary instances, already referred to, of those higher forms which have left traces of their existence in palæozoic times, it is evident that, from the Carboniferous strata downwards, we have to deal for the most part with three great groups of Crustacea, namely the Merostomata, the Trilobita, and the Entomostraca.

The first of these, the Merostomata (or thigh-mouthed

* I believe the form I have described under the generic name of Necrogammarus, from the Lower Ludlow, to be an Amphiphod. See "Trans. Woolhope Club, Hereford," 1870, p. 271.

† I have described a part of a giant Crustacean, which I believe to be an Isopod, under the name of Præarcturus gigas, from the Devonian of Herefordshire. See "Trans. Woolhope Club, Hereford," 1870, p. 266.

‡ Pyrgoma cretacea, H. Woodward, "Geol. Mag.," 1868, Vol. V. p. 258, pl. xiv. figs. 1, 2, 3. From the Upper Chalk near Norwich is at present the oldest.

§ Turrilepas Wrighti, H. Woodward, "Quart. Journ. Geol. Soc.," 1865, Vol. XXI. p. 486, pl. xiv. figs. 1–6.

Neolimulus falcatus, H. Woodward, "Geol. Mag.," 1868, Vol. V. p. 1, pl. i. fig. 1.

CRUSTACEA

Turri

Neolimulus Pterygotus