SPIROLOCULINA PLANULATA. 105 



" turgidula " would have been applicable if we knew the specimen, but for those 

 varieties having more or less convex chambers we must take "nitida" — 

 d'Orbigny's earliest name. The flat-chambered forms, however, remain as Sp. 

 planulata, whether oval or round in outline, and whether square or rounded on 

 the margin or even slightly channelled, as in our PI. Ill, figs. 37, 38. They are very 

 liable to vary in relative thickness. Some specimens become somewhat concave 

 by a step-like arrangement of the flat chambers rising one higher than the other 

 during the growth of the shell. 



Other varieties of Sp. planulata have the surfaces of the chambers slightly con- 

 cave, such as are well shown in Sp. Badenensis, d'Orb., and $p. dilatata, d'Orb. 

 These, moreover, being somewhat concave in the middle, are evidently passage- 

 forms leading to Sp. excavata, d'Orb. 



The following have the chambers slightly hollowed, the shell, however, remain- 

 ing flat : Sp. cretacea, Reuss, and Sp. compressiuscula, Karrer. 



Some of the planulata- group forms are very thin (such as the compressiuscula, 

 K., and papyracea, B. S. B.). Of the flat-chambered forms our figs. 37 and 38, in 

 PL III, represent an extreme example (with slightly fluted margin), but are well 

 matched in Brady's Report ' Challenger,' pi. ix, fig. 11 (with plane margin). 



Occurrence. — As a shallow-water form Spiroloculina planulata has a wide 

 geographical range in temperate latitudes. It has been recorded as a fossil from 

 the London Clay, the Calcaire grossier of the Paris basin, the Miocene of Vienna, and 

 the Tertiaries of Palermo. In the Crag it has been found at Sutton only. In the 

 First Part of this Monograph it is stated to occur commonly there ; but in our 

 material we have not been able to find a single specimen from Sutton or 

 elsewhere. 



Mr. Millett observes that — 



Spiroloculinje having plane chambers with ornamented surfaces are — 



Spiroloculina costigera, Terquem, 1882. Mem. Soc. Geol. Fr., ser. 3, vol. ii, 



p. 159, pi. xxiv, fig. 24. 



— pertusa, Terquem, 1882. Ibid., ser. 3, vol. ii, p. 100, pi. xxiv, 



fig. 27. 



— semiornata, Terquem, 1882. Ibid., ser. 3, vol. ii, p. 161, pi. xxiv, 



fig. 28. 



