pai't 3] A^'D STEUCrrRE of the FORAMINIEEEAL SHELIv. 211 



The Imperforata retain their structure witli similar persistency. 

 Thus the Miliola of the ' Calcaire Grossier ' and Leitha-Kalk 

 scarcely differ in this respect from existing forms, and the same is 

 true of species belonging to this genus, which occur in the phos- 

 phatic nodules of the Cambridge Green sand. 



The foraminifera which are associated with Saccammina carferi 

 in the thin slices I have examined include porcellanous forms, such 

 as Endoflii/ra, which retain their original structui*e with but 

 slight indications of mosaic growth, and vitreous forms, such as 

 ArchcediscKS, which still display their characteristic Nummuline 

 perforation. Both offer a striking contrast to Saccammina carferi, 

 and consequently the mosaic structure of its wall may be regarded 

 with great probability as being original. 



The fossil may, then, have been an arenaceous form, but there 

 is much to suggest that it was not. Such irregular fragments of 

 calcite as now form the mosaic of its wall do not occur in the muddy 

 part of the Saccammina Limestone, and are not likely to have formed 

 part of the ooze of the sea-floor on which the animal lived ; and, what 

 is more important, we have already discovered in an example of 

 Spirillina vivipara a mosaic structure not unlike that which occurs 

 in Saccammina carferi. It is possible, therefore, that the alliance 

 of this fossil is rather with the Calcareous than the Arenaceous 

 Imperforata. That it should bear a name which identifies it, 

 perhaps on insufficient evidence, Avith a living genus is unfortunate 

 and may lead to confusion. To avoid this, I propose to make the 

 least possible change by calling the genus S a c c ammi n op s i s. 



In conclusion, I should like to express my warm thanks to my 

 friend and colleague, Mr. T. Vipond Barker, for the kindly 

 assistance which I have received from him in the course of this 

 investigation. 



EXPLANATION OF PLATE VII. 



Fig. 1. Part of a horizontal section of Orhitolites cotwplanatiis showing the 

 fibrous structure of the walls. X 90. (See p. 199.) 



2. A similar section photographed between crossed nicols. X 90. 



(See p. 200.) 



3. A similar section more highly magnified. X 140. 



4. A similar section of a larger area, between crossed nicols. X 55. 



(See p. 200.) 



5. A similar section showing, as a thin black line, a layer parallel to 



the wall of the chamber, which remains extinguished between 

 crossed nicols during a complete rotation of the stage. X 140. 

 (See p. 205.) 



6. Part of a horizontal section between crossed nicols. X 90. (See 



p. 200.) 



Figs. 7 & 7 a. Spirillina vivijjcira Ehrenberg, seen in optical section ; 

 fig. 7x54, fig. 7 aX 95. (See p. 208.) 



Fig. 8. Section of Saccainmhia (SaccamminopsisJ carteri, showing below the 

 included matrix (black), on the right a quartz-mosaic, ending in a 

 border of chalcedony ; this is sharply bounded by calcite which 

 completes the infilling of the interior. Except where it is in con- 

 tact with the included matrix, the structure of the shell is 

 destroyed by silicification. Xl6. (See p. 195.) 



