| Fig. | 1.— | Limulus Rotundatus, the imprint of fig. 3. |
| 2.— | The nodule before it was broken. | |
| 3.— | Limulus Rotundatus, (the corresponding portion of the nodule, fig. 1,) showing the entire form of the carapace. |
FOSSIL LIMULUS.
The Limulus (Mollucca or King Crab) is a genus belonging to that Division of the Entomostraca termed Pœcilopoda and is abundant in the seas of India and America. The carapace is crustaceous and of a semilunar form, the head and thorax are blended together, and the superior abdominal shield, which is composed of confluent segments, appears like one piece, and has an indistinct trilobed character; the last segment is prolonged into a three-edged, sharp, styliform weapon. The Limulus has two reniform, compound eyes, composed of facets of a peculiar form. The gills are disposed on lamelliform processes. It is distinguished from all other crustaceans by the mastication of its food being performed by the first joint of the thoracic legs which surround the mouth, instead of by jaws.
Lign. 173. Limulus trilobitoides.
Coal Measures. Coalbrook Dale.
Very fine examples of a fossil species of this remarkable genus are occasionally obtained from the lithographic stone of Solenhofen.[450] In England three small species have been discovered in nodules of ironstone and indurated clay, in the Carboniferous strata of Coalbrook Dale, by Mr. Prestwich.[451] In one example (L. Anthrax[452]) two of the legs are seen extending from under the body; in another species the sharp, pointed process of the tail is well developed (Buckl. p. 396, and tab. xlvi″.; see also [Lign. 173]). The specimen figured [Lign. 172] is one of several examples which I obtained by breaking up nodules from that celebrated locality. Fig. 2 represents the nodule unbroken, and without any indication of its contents; by a well-directed blow it was separated into two equal portions, figs. 1 and 3, in which the carapace of the crustacean, and its marginal appendages, are well displayed. The rounded form of the carapace, and the membrane which appears to connect the spines, separate this species from all others.
[450] Hist. Crust. Foss. pl. xi. fig. 6.
[451] See Mr. Prestwich’s Memoir on the Geology of Coalbrook Dale, Trans. Geol. Soc. second series, vol. v. part 3.
[452] Trans. Geol. Soc. second series, vol. v. pl. xli. figs. 1-4.