MILIOLININiE. 91 



succinct account of dimorphism in the two different senses in which it had been 

 applied by Rhizopodists from the time of d'Orbigny to that of Munier-Chalmas 

 and Schlumberger. 



The structural differences, among the Miliolidse and others, discovered and 

 illustrated by MM. Munier-Chalmas and Schlumberger are of very great interest, 

 adding much to our knowledge of Foraminifera. They are often associated with 

 external features sufficiently recognisable for the use of the trivial names already 

 in vogue, and the zoological standing of the members of the group is not 

 interfered with. Indeed, their mutual relationships have strong evidence in the new 

 observations. Thus the structure of Biloculina depressa, form B, shows that this 

 form passes through (1) a biloculine, (2) a triloculine, (3) a quinqueloculine, and 

 (4) a biloculine stage in reaching completion ; whilst B. comata has (1) a biloculine, 

 (2) a quinqueloculine, (3) a quadriloculine, (4) a triloculine, and ultimately (5) a 

 biloculine stage. Adelosina, after its unilocular form, has biloculine, triloculine, 

 quadriloculine, and quinqueloculine stages. This is termed " initial poly- 

 morphism " by MM. M.-Chalmas and Schlumberger. Not only is the real generic 

 value of MiUolina thus more firmly established, but it has a right to include 

 Biloculina and Sjnrolocidina (as applied by Dr. A. Goes). 1 



M. Schlumberger states that in the Biloculinse and Triloculinse having a small 

 initial chamber (the form B) the first chambers are as in Quinqueloculina ; 

 subsequent chambers take the arrangement that they have in the other form (A) 

 of each of the two genera, namely, on two planes or surfaces of symmetry for 

 Biloculina, and on three for Triloculina. He observes (' Bullet. Soc. Zool. 

 France,' vol. xi, 1886, p. 557), " In the three species of Adelosina under notice, 

 and in the three groups of Biloculinse already mentioned, the form B presents a 

 special character common to all the individuals of each of the groups. In the 

 Adelosinse this is a megasphere completely enveloped by the first chamber, which 

 becomes lenticular. In the Biloculinse it is the megasphere with two series of 

 chambers on two planes of symmetry. I could cite also the TriloculinsB and the 

 Quinqueloculinae, in which the megasphere is encircled with three or with five 

 series of chambers. 



" In the form B of these four genera, on the contrary, the microsphere is 

 always encircled with a cycle of five chambers ; and this grouping is sometimes 

 regularly or irregularly persistent, and sometimes it is differently arranged. 



" I conclude, then, that, in the classification of the MiUolidm, a megaspheric 

 form (A) will determine the genus, and the microspheric (B) the species." He 

 also mentions that many of the Quinqueloculinse are of the genus Adelosina. 



* The thickening of the shell- walls in various degrees, forming labyrinthic 

 interiors and cribriform apertures, already noticed in Miliolidse, as in Lituolidse and 



1 ' K. Svenska Vet.-Akad. HaDdl.,' vol. xix, No. 4, 1882, pp. 122—132. 



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