46 MK. F. CHAPMAN ON SOME [Jan. 15, 



section, the umbonal centre being more prominent on one side 

 than the other. This fact points to the tendency of this species 

 to increase in an obhque or turbinoid spiral, such as is shown in 

 all undoubted Amphiateghue and not on the Xummuline plan. T 

 venture to suggest that the peripheral figure of this form, as 

 originally given by Fichtel and Moll ', is too symmetrically drawn, 

 and it is easy to conceive how such a slight degree of asymmetry 

 would be overlooked without the accompaniment of carefully 

 pi-epared sections of the test. 



Another feature, moreover, brought out in the transyerse 

 sections of the test, and which helps to strengthen the evidence in 

 favour of this form belonging to the genus Amphistegina, is the 

 existence of the characteristic double cone-shaped non-tubulate 

 portions of the test which form its central axis in transverse 

 section (see Plate I. fig. 9). 



Whilst examining the median sections of A. racUata, the presence 

 of true interseptal canals with many brauchlets was detected 

 (see fig. 10). In his ' Introduction to the Study of the Forami- 

 nifera,' Dr. Carpenter describes the various characters which 

 distinguish forms of the genus Amphistegina, and of which a 

 summary and comparison with the Eotaline type is given at 

 p. 246. Here it is remarked that the " singleness of the septal 

 lamellae is a most important additional link of affinity " to the group 

 of the Eotahnes. This statement, which may have been made 

 through the examination of non-typical specimens, caused me some 

 doubt as to the Aalidity of the claim of A. radiata to the Amphi- 

 stegine group. Upon preparing sections of typical specimens of 

 AmpJiistegina hauerina from the Vienna Basin, which 1 possess 

 through the kindness of Professor T. Eupert Jones, I found the 

 same well-developed canal-system existing in the fossil forms (see 

 fig. 11), of the true position of which as AmpJnstegvun there can be 

 no question, as were seen in the recent specimens of A. radiata. 



Therefore that apparently serious objection was satisfactorily 

 removed, and, at the same time, additional facts were obtained, 

 which show that, as far as the shell-structure is concerned, 

 Amphisfegina is as highly advanced in differential characters as is 

 the shell of Xummidina. The only difference therefore that 

 appears to exist between ordinary Ampliistegbup of the A. lessomi 

 type (including A. hauerina) and the recent A. radiata is the 

 remarkable modification of the segments in the former type of the 

 outer layer on the inferior side of the test giving rise to the 

 " astral lobes." 



The transverse sections of the Amphistegincp generally, if taken 

 accurately through the middle of the shell, exhibit the large 

 spherical primordial chamber with the succeeding more or less 

 ovoid one. I especially mention this fact since several examples of 

 the young tests of A. radiata have occurred in the peripheral whorls 

 of adult specimens of that species, and are seen in both median and 



' Ojj. cil. pi. viii. fig. d. 



