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. 



