Page:AmJourSci 4 38 228 507-510.djvu/2

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Barbour—Carboniferous Eurypterids of Nebraska.

whorls closely imitate pale yellow flowers pressed in the shale. The association of land plants with eurypterids has been observed before. They suggest the probability that this group, the sea scorpions, which originally were distinctly marine, had undergone adaptive modifications suiting them to a brackish, or even fresh-water habit.

Intimately associated with the eurypterids were considerable amounts of actual plant tissue, preserved as such since Carboniferous times. It still retains its pliability, can be stripped from the shale, floated on glass slips, and made into permanent mounts. There are now about one hundred of these mounts in our collection. The preservation of actual plant tissue in such amounts and in large pieces is quite unique. The tissue is of a bright, transparent orange color. It is capable of close study, and photomicrographic reproductions of the cell structure are readily obtainable. This matter will be made the subject of a special leaflet.

As compared with well-known eurypterids, those of Nebraska are small, the average being a trifle over two inches in length, while the largest, as far as known, do not equal three inches. Whether these represent adult or immature forms, is not apparent. They may be immature forms. However, since no evidences of larger individuals have presented themselves, it may be that this is a group of diminutive eurypterids. Average eurypterids are five to ten times as large. The presumption is that many of the specimens at hand are exuviæ.

The prominent feature of any eurypterid is its scorpioid outline. It has a broad flat head, two broad paddles, and a long segmented abdomen or body tapering towards the tail, which usually ends in a sharp spiniform telson. The head-shield is commonly semi-circular, or, in some instances, somewhat quadrate. It bears two prominent compound eyes, and certain simple eyes, or ocelli, which are generally obscure. The head-shield probably enabled Eurypterus to shovel and burrow as does the horseshoe crab when in pursuit of marine worms. The jawless mouth of Eurypterus is centrally located on the ventral side of the cephalothorax, and is surrounded by six pairs of appendages, some of the bases of which are so serrated, spined, and dentated, as to serve functionally as jaws, or maxillipedes.

The appendages aside from the paddles are rather inconspicuous. The paddles are greatly enlarged for swimming, and perhaps for roiling water to conceal and protect the creature. The paddles are evidence, rather than proof, of active swimming habits. In fact, Eurypterus may have been rather sluggish, content perhaps with grovelling. Its life habits may be inferred from the closely related form, Limulus.