14 HALKYARD, Fossil Foraminifera of the Blue Marl 



"espece renflee et striee"' and his drawing from the Planche 

 inedite as reproduced by Fornasini (F. 1905, S.O.M. p. 63. 

 pi. II. fig". 9) shows no pitting, nor is any visible on d'Orbig- 

 ny's type specimens which we have examined both in Paris and 

 at La Rochelle. Terquem's figure has now become however 

 so generally accepted for a determinate type that it seems im- 

 possible to depart from it. It must be borne in mind that he 

 also had examined the d'Orbigny types and plates in Paris * 



Yet another type with fairly distinctive features has been 

 ascribed to this species by Millett (Millett, 1898, etc., F.M. 

 1898, p. 504, pi. XII; fig. 1 a, b, c). This represents a form 

 with regular cross bars between longitudinal costae, the 'de- 

 pressions thus formed being apparently regarded as analagous 

 to the pits in the Parisian Eocene type of Terquem.) 



Genus Sigmoilina, Schlumberger. 

 22. Sigmoilina tenuis (Czjzek), 



Quinqueloculina tenuis, Czjzek, 1848, Haidinger's Nat. Abh., 



vol. II, p. 149, pi. XIII, figs. 31-34. 

 Spiroloculina tenuis, Brady, 1884, Chall. Rep., p. 152, pi. X, 

 figs. 7-1 1. 



Found frequently and well-preserved through the whole 

 thickness of the marl beds. 



(The species is represented by an exceptionally fine series 

 of specimens. The propriety of transferring the species from 

 Spiroloculina to Sigmoilina is we think open to question, 

 especially when such a large and varying collection as the 

 present one is considered. The Sigmoilina curve is of the most 

 rudimentary nature, although it is apparent in some of the many 

 broken sections which have been mounted for the purpose of 

 displaying it. In the majority of specimens especially in some 

 Gatherings (notably G. 8) where the specimens are exception- 

 ally large there is hardly the faintest deviation from a typical 

 spiroloculine growth. It is very curious how this delicate little 

 Miliolid has, generally speaking, escaped the erosion from 

 which the other Biarritz Miliolids suffer. If Halkyard's theory 

 of the disappearance of the Miliolid shell owing to a difference 

 in its molecular composition, as compared with the shells of 

 the perforate Foraminifera, is correct (see his Introduction) it 

 points to a further difference in the constitution of the test of 



* See O. Terquem, " Foraminiferes de 1' Eocene de Paris," Mem Soc. Geol. 

 France, S.3, ii, Mem. 3 p.n and E. Heron-Allen, "Alcide d'Orbigny," J. R. Mier.. 

 Soc. Presidential Address, 1917, p. 33. 



