The specimen was obtained from a mass of quartzite, and rests enclosed in a portion of the body- chamber of a Nautilus imperialis.
2. Rhachiosoma echinata, sp. nov. (Plate IV. fig. 5.)
This handsome crustacean, which must have measured 3| inches from tip to tip of its lateral spines, and 1| inch from the anterior to the posterior border of its carapace, is far more robust than the preceding species. The hepatic spines are only an inch in length, and develope a small branch spine midway upon their anterior border, resembling in this character the hepatic spines of Psammocarcinus Hericartii (see Plate IV. fig. 4).
The arrangement of the tubercles agrees with that in the foregoing species (R. bispinosa), save that around the central tubercle on the cardiac region there are placed three very minute tubercles, whilst two others, equally minute, mark the metacardiac region. The latero- anterior border gives evidence of three marginal spines on either side, all of which, however, have been broken off. The frontal border is quite lost, although most carefully attempted to be worked out by an experienced hand ; the extreme hardness of the matrix (a fine-grained and very hard quartzite), as in the former case, defying development. Where the surface of the carapace has been preserved it is finely punctate. The chelate fore-hand is preserved on the right side, exhibiting 3 joints, and measuring about 1-3/4 inch in length.
EXPLANATION OF PLATE IV.
Fig. 1 a. Dorsal aspect of carapace of Paloeocorystes glabra, H. Woodw. (nat. size), from the Lower Eocene, Portsmouth.
Fig. 1 b. The same, seen from the underside : m. maxillipede ; br. branchiostegal piece.
From the Cabinet of Caleb Evans, Esq., F.G.S.
Fig. 2. Paloeocorystes (Notopocorystes) Mulleri, Binkh. (two-thirds natural size), from the Uppermost Chalk, Maestricht. (Copied from tab. is. fig. 1 b, Mon. des Gasteropodes et des Cephalopodes de la Craie Superieure de Limbourg, by J. Van den Binkhorst, 1861 ; figured for comparison with P. glabra.)
Fig. 3. Rhachiosoma bispinosa, H. Woodw. (nat. size), from the Lower Eocene, Portsmouth. From the Cabinet of C. J. A. Meyer, Esq., F.G.S.
Fig. 4. Psammocarcinus Hericartii, Desmar., sp. (twice nat. size), from the Sables de Beauchamp (Lower Eocene). (Copied from the Hist, des Crustaces Podophthalmaires Fossiles , by Alph. Milne-Edwards, tome i. pl. 10, fig. 1. Paris, 4to, 1861).
Fig. 5. Rhachiosoma echinata, H. Woodw. (nat. size), from the Lower Eocene, Portsmouth.
From the Cabinet of C. J. A. Meyer, Esq., F.G.S.
3. On the Chalk of the Cliffs from Seaford to Eastbourne, Sussex. By W. Whitaker, Esq., B.A. (Lond.), F.G.S.*
- This paper has been withdrawn by the author by consent of the Council.
