SPIROLOCULINA EXCAVATA. 107 



is sunken in the centre and biconcave ; sutures sometimes limbate ; edges thick, 

 and the margins plane, or nearly so. 



In this form the chambers gradually increase in thickness from the first to the 

 last, so that the inner or central part of the test is hollow and thin, and the outer 

 is thick, with more or less projecting edges. 



Our form, PI. V, fig. 2, is very similar to d'Orbigny's representation of the 

 Vienna fossil. Some specimens are more oval and produced at the ends. 



As in other cases, some confusion has arisen about the " species," which is 

 essentially a biconcave variety of Spiroloc. planulata. 



Of three figures given by Soldani, ' Testaceogr.,' vol. ii, 1798, pi. xix, figs. I, m, n 

 (p. 54, Frumentaria Sigma et Bhombos), d'Orbigny chose one (fig. m) for his 

 Sptroloculina limhata ('Ann. Sci. Nat.,' vol. vii, 1826, p. 299, No. 12). This is a 

 nearly oval Spiroloculina, with the outer chambers apparently rounded, and 

 one of them much inflated ; the centre is concave. No limbation is shown. 

 This shell is noticed in the ' Ann. Mag. Nat. Hist.,' ser. 4, vol. viii, 1871, p. 248, 

 No. 141, pi. 8, fig. 22, by Parker, Jones, and Brady, as "a bold variety [of 

 Spirolomlina planulata] with inflated chambers." The figure there given 

 unfortunately does not express the convexity or roundedness of the outer margin 

 of the chambers, but makes them flat and sharp-edged. If all the chambers had 

 a definitely convex surface, this shell would be allied to the Sp. nitida and 

 rotunda, d'Orb. As it is, the fig. m may be referred to 8p. excavata. 



Of the two other figures, fig. / is oval and concave, with flat chambers ; and 

 fig. 11 is like it, but of a narrow-oval outline. These two correspond suflBciently 

 well with Sp. excavata, as figured by d'Orbigny, ' Foram. Foss. Vien.,' 1846, 

 p. 271, pi. xvi, figs. 19 — 21. Fig. m is rightly referred by Signer C. Fornasini, 

 'Bollett. Soc. Geol. Italiana,' vol. v, 1886, p. 238, No. 368, to Sp. excavata, d'Orb., 

 but we should think, if Soldani's drawing be true, as a sub-variety (such as 

 inasqualis) of that form. 



Occurrence. — Spiroloculina excavata has its home in comparatively shallow 

 water ; and it is, for the most part, confined to tropical and the warmer temperate 

 seas. Fossil specimens are recorded from the London Clay of Sheppey, the 

 Miocene of Vienna, the Pliocene (?) of Italy, and the Pliocene Clay of St. Brth. 

 In the Cra^: we find it at Sutton and Broom Hill. 



15 



