The Chalk contains a few species of the Macrura, which were first discovered in the quarries near Lewes, and are figured in Foss. South D. tab. xxx. xxxi.; they are among the most rare and delicate of the fossils of the Cretaceous strata. These remains consist of the carapace and claws, and rarely of the tail and antennæ, and are composed of a friable earthy crust, which, when first discovered, is of a dark chocolate colour, but quickly changes to a pale fawn, or reddish brown, by exposure to the air. In the specimens obtained by breaking the stone, the crustaceous covering remains attached by its rough external surface to one portion of chalk, and on the corresponding piece are sharp casts of the carapace and claws, having a glossy surface covered with minute papillæ formed by the bases of tubercles or spines. Four species have been observed.
Enoploclytia Leachii. [Lign. 169], figs. 1, 2, 3.—This is a long delicate crustacean, having a pair of equal, slender, anterior chelate claws, the fingers of which are long, attenuated, and armed with a row of obtuse cylindrical spines. The surface of the hand-claws is muricated, or covered with short erect aculeated tubercles. The pincers in the specimen figured [Lign. 169], fig. 3, are shorter than in most examples. The carapace is elongated and sub-cylindrical, with a dorsal ridge and two lateral furrows, indicating the normal division of the cephalic and thoracic segments of the shield; the antennæ are long, filiform, and setaceous (bristly), and are placed on squamous peduncles (see [Lign. 169], fig. 2).
There appear to have been five legs on each side; the anterior or chelate pair are the most usual relics of this animal; of the other claws and the branchiæ, but obscure indications have been obtained. The abdominal segments are arcuate, and six or seven in number; their surface is granulated; the appendage, or tail, is foliaceous and marginate, with a few longitudinal ridges (see [Lign. 169], fig. 1).[442] The claws of these crustaceans may be easily recognised by their general aspect, and the length and straightness of the fingers or pincers. In most examples traces remain of the tendinous expansion of the muscles of the moveable claw (see [Lign. 169], fig. 3).
[442] See Foss. South D. p. 221, et seq. for further details.
Lign. 169. Fossil Crustaceans: nat. Chalk. Lewes.
| Fig. | 1.— | Abdominal appendage, or tail, of Astacus[443] Leachii (G. A. M.), with three abdominal segments. |
| 2.— | Part of the head of Astacus Leachii, with remains of the squamous peduncles of the antennæ, and of the long setaceous antennæ. | |
| 3.— | Chelate claw, with part of the carpus, or wrist, of Astacus Leachii. | |
| 4.— | Chelate claw of Astacus[443] Sussexiensis (G. A. M.). |
[443] These fossil Lobsters are now to be referred to Prof. M’Coy’s genus Enoploclytia.