470 HE. Neaverson—Foruminifera of the Hartwell Clay. 
of Cristellarians. In these deposits the ensiform Cristellarians 
abound, whilst the rotulate varieties (which predominate in the 
Hartwell Clay) are subordinate. The occurrence (though rare) of 
Cristellaria gracillissima in the Oxford Clay is noteworthy, as its 
previous lowest record is from the Speeton Clay of Yorkshire 
(Sherlock, 1914). The only common Vaginulina in the Oxford and 
Kimmeridge Clays of Bucks is V. harpa, though V. discors also 
occurs. These belong to the group with strong longitudinal ribs 
which, according to Berthelin, had its maximum development in 
Jurassic times. Marginulina linearis occurs in both the Hartwell 
Clay and the Oxford Clay of Bucks; this is the first record of the 
species below the Speeton Clay. 
A noteworthy feature of the Oxford Clay Foraminifera from 
Quainton is the great abundance of the arenaceous form, 
Haplophragmium cf. cequale, which exceeds in numbers all the 
other species collectively. In the Hartwell Clay arenaceous forms 
are uncommon. Porcellanous forms are not found in the Hartwell 
Clay, but the Gault of Ford is remarkably rich in Spiroloculina and 
Miliolina, whilst Vitriwebbina irreqularis is abundant in the Oxford 
Clay of Quainton. Thus the main features of the foraminiferal 
assemblages may be tabulated as follows :— 
Bucks, deposits.) Cristellaria. Vaginulina. Arenacea. Porcellanea. 
Rotulate Limbate and Rare. Spiroloculina and 
varieties. marginate. Miliolina. 
Hartwell Clay. | Rotulate Longitudinally Rare. None. 
varieties. ribbed. 
Oxford Clay. Ensiform Longitudinally Haplophragmium cf. | Webbina irregularis 
varieties. ribbed. equale, abundant. Auctt. 
A distinctive feature of the Hartwell Clay assemblage is the 
frequent occurrence of Cristellaria fragraria, which has hitherto 
been regarded as a characteristic Tertiary form. It is common at 
two horizons in the Hartwell Clay, and specimens from the higher 
bed show a more advanced degree of outcoiling than those from 
the lower. The occurrence of similar forms at widely separated 
horizons suggests that these forms should not be included under 
the same specific name They may be “ morphic equivalents” 
arising from different stocks and thus analogous with homceomorphic 
forms of Ammonites which are at least generically distinct. This 
question cannot be decided until more is known of the evolution 
and development of the Foraminifera. 
The Tithonian Stramberg limestone, a deposit of approximately 
the same age as the Hartwell Clay, contains fourteen species belonging 
to seven genera.' The dominant forms are two arenaceous species 
(Ammodiscus incertus and Involutina remesiara) and the cosmopolitan 
* Chapman, Linn. Soc. Journ. Zool., vol. xxviii, 1900, p. 28. Perner, Bull. 
Acad. Sci. Bohéme, 1898, p. 1. 
