Page:Quarterly Journal of the Geological Society of London, vol. 33.djvu/248

200 200 J. S. GARDNER ON BRITISH CRETACEOUS PATELLIDJE ETC.

It was discovered in the Upper Chalk, at Norwich, and is pre* served in the Woodwardian Museum at Cambridge.

EmARGINULA AFFIX1S, Sby.

This is probably identical with E. sanctce-catliarince. It is figured in Dixon's ' Geology of Sussex/

Punctfrella antiqua, sp. nov. Upper Greeiisaud. PI. IX. figs. 6-9.

Conical, cap-shaped ; apex blunted, excentric ; anterior region inflated, posterior hollowed out ; shell thick, ornamented with about 60 radiating ribs, which become finer towards the posterior region. The cast presents posteriorly a central groove or depression extend- ing from margin to summit. In this depression is a longitudinal, narrow, fissure-like scar, extending from the margin about § of the way up, and terminating above, at the deepest part of the depression, in a small, raised, pipe-like protuberance, which has filled in the perforation. The second specimen figured does not show the depression so prominently ; but in this case the shell is not completely removed, and still partly fills it up ; the scar, however, is present. The depression has been caused by the internal shell) r plate, characteristic of the genus, which answers probably a some- what similar purpose to that of the internal septum in other genera. Some of the Eocene Fissurellce are also thickened at the foramen, which is then excentric ; but in Fissurella the fissure, if not apical, is immediately under and in front of the apex, whilst in Punctu- rella it is always placed behind the apex.

These specimens, which are from Devizes, are of especial interest, as they carry far back into Cretaceous times a genus which had hitherto not been met with fossil except in Glacial deposits. There are but few living Puncturellce ; P. cucullata, from Oregon, is the nearest known representative of our species. The specimens are in the British Museum.

The genus Fissurella is not represented ; and its absence is the more remarkable as nine species are recorded from foreign Creta- ceous rocks, and it is well represented in the Tertiaries. It may be noticed, as a possible explanation of the absence of both Patella and Fissurella, that the strictly littoral habits of these two great genera may have precluded their being buried, under ordinary condi- tions, with other Mollusca, in the deeper Cretaceous seas. The genus Emarginula, on the contrary, is a deep-water form, and is found more or less abundantly in most of the divisions of the Neocomian, Upper Grecnsand, and Chalk. Its absence in the Gaultis confirma- tory evidence of the shallowness of that sea, whilst its presence in the Upper Gault of Switzerland agrees with the character of the associated fauna. The scarcity of living species of Emarginula and their former abundance, has led to the idea being expressed by several authors that it is dying out and being replaced by Fissurella. The genus Pimula, not uncommon in the Oolites, is still unrepre- sented in subsequent rocks until it is met with in the Tertiaries.

The family of Siphonariidag is only represented in Cretaceous times by S. antiqua, Binkhorst, from the Upper Chalk of Limburg.