﻿TROCHAMMINA. 



79 



cession of palaeontologists. Increased knowledge of the arenaceous group of Foraminifera 

 has led to a better understanding of such simple forms; and Messrs. Jones, Parker, and 

 Kirkby's paper on the " Permian Trochamminae," before referred to, will be generally 

 accepted as setting at rest the doubt which has existed as to the relationship of the group. 

 Of the various drawings of the species given by these authors (see figs. 2 — 6 of their 

 plate, loc. cit.) numbers 2 and 3 may be regarded as transitional, taking positions between 

 Tr. incerta and Tr. pusilla, whilst figs. 4 and 5 represent the full characters of the latter, 

 and fig. 6 a specimen verging towards Tr. gordialis. Of the two drawings of Trocham- 

 mina pusilla given in Plate III of the present work, fig. 5 is from the Magnesian 

 Limestone (Permian) of Tunstall Hill, near Sunderland, whilst fig. 4 is a Carboniferous 

 specimen from one of Mr. Robertson's Scotch gatherings. The latter is an unusually 

 fine example, and possesses a somewhat singular character in the fringe of white 

 subarenaceous shell-substance which lines the inner border of the convolutions. This is 

 probably the effect of luxuriant growth, but I do not recollect having seen any other 

 example of an arenaceous Foraminifer with precisely the same kind of limbation. 



Distribution. — Though isolated specimens have been found by Mr. Robertson in a 

 single locality of the Lower, and in one locality of the Upper Carboniferous Limestones 

 of Scotland, Trochammina pusilla is essentially a Permian species. It occurs abundantly 

 in the Lower and Middle Magnesian Limestones of England, and in the Kupferschiefer, 

 Zechstein proper, and Middle Zechstein of Germany. Its presence in Ireland, in the 

 bed regarded as pertaining to the Upper Magnesian Limestone, has also been recorded, 

 but it does not seem to have been observed elsewhere in the highest division of the 

 Permian rocks. 



Trochammina milioloides, Jones, Parker, and Kirhby. PI. Ill, figs. 11 — 15. 



Trochammina milioloides, Jones, Parker, and Kirkly, 1869. Ann. and Mag. Nat. 



Hist., ser. 4,vol.iv, p. 390, pi. xiii, figs. 9 — 14. 



Characters. — Test free, convoluted ; oblong or broadly oval, compressed. Convolutions 

 on one plane, few, broad, embracing. Aperture varying in form, corresponding to the 

 transverse section of the tube, or only slightly constricted. Length ^th inch 

 (175 mm.). 



The intermediate Trochammina, to which the name Tr. milioloides has been assigned, 

 bear the same sort of relation Tr. pusilla that the Biloculine and Triloculine Miliolce 

 bear to the Quinqueloculine and Spiroloculine. The name is put forward by its authors 



