204 J. S. GARDNER ON BRITISH CRETACEOUS PATELLIDJ3 ETC.
This is the only patelliform Gastropod from the well-known Blackdown beds, and is unique. The original is in the British Museum.
The shells of Pileopsis are very variable, attaching themselves to foreign objects, of which they frequently take the impression, as in the case of strongly radiated bivalves &c. P. squamceformis, from the Paris-basin Eocene, takes the crescentic form of the aperture of Fusus longcevus when fixed inside the aperture of that shell. The genus is peculiarly interesting geologically, being the nearest repre- sentative of the Silurian cap-shaped shells, which range upwards to the Lias. Although absent in the Jurassic, it is well represented in the Lower Cretaceous rocks, Pictet and Campiche enumerating ten species in their list.
Hipponyx Dixoxi, Deshaycs. Upper Grcensand and Chalk. PL IX. figs. 12, 13.
Shell-base in the form of a solid cylinder of irregular growth, at the extremity of which is apparent the peculiar muscular impres- sion special to the genus Hipponyoc.
The name was suggested by Deshaycs for the irregular body figured in Dixon's ' Geology of Sussex,' pi. xxvii. fig. 8, without specific description or name. Similar specimens are not uncommon in the White Chalk, and are preserved in most collections. Eocene and Recent forms alike sometimes deposit a scries of bases, one over another, but none to the same extent, or so shiftingly, as appears in the Cretaceous form. It may be that, as at the bottom of the Chalk sea stones or rocks were rare, the excessive and heavy deposit served the animal in lieu of them, and formed an anchorage ; the shifting may have taken place to escape burial or silting-up. The Greensand specimen from Cambridge, in the "Woodwardian Museum, is very solid, the last base being deeply hollowed out, like a basin.
The genus makes its first appearance in Cretaceous rocks, and is met with in the Chalk of Normandy and the Maestricht limestone. Capulus dunkerianus, D'Orb.,is the only upper valve yet discovered which could belong to these bases .
EXPLANATION OF THE PLATES.
Plate VII.
Figs. 1, 2. Pileopsis neocomiensis, sp. nor. Lower Greensand. Tealby ;
Woodwardian Museum. Figs. 3, 4. Crucibulum gigantcum, sp. nov. Neocomian. Shanklin ; Jer-
myn-street Museum. Figs. 5, 6, 7. Pileopsis Seeleyana, sp. nov. Blackdown ; British Museum.
(Fig. 5, magnified.) Figs. 8, 9. Helcion Mcyeri, sp. nov. Magnified. Lower Greensand ; Mr.
Meyer's collection. Figs. 10, 11. The same, natural size. Figs. 12, 13, 14. Crepidula chamceformis, sp. nov. Neocomian, £eend ;
British Museum. Figs. 15, 16. Scurria ealy piriformis, sp. nov. British Museum.
