MANGANESE OF THE LAMELLII5RANCH-. 165 



fn>m o.i.} i" i-*4 per cent, of the dry weight. It has thus been 



obtain, through the agency of these organisms, several 



gram- \ manganese from running water which contained about 



r rent, of that element. The concentrating effi- 



eiei. lower forms is therefore of a high order. 



1 1, in;.; the shell, the Unionida? deposit salts of man- 



-.iii' '11 as of calcium and magnesium. The nacer of 



tin- -lull-, r.iivtully freed from contaminating material, al\va>s 



ion for manganese; its presence in the shell 

 ts its presence in any of the tissues. It was 

 Him -lore that an examination of fossil shells <>t the 

 \\onld be of interest in determining whether the man- 

 ganese i- "t < mparativdy recent occurrence in these animals 

 r \\liether it i- a metabolic characteristic of long standing. 



\\ II.IM- h.il the opportunity to examine but one well pr< - 



il -hell. This was a specimen obtained through the 



c.nii if Dr. G -e Wagner who published a description 



..I it in .\<:ii!i!in. \'ol. iK. The nacer of this shell was perfectly 



retaining its luster, though friable and crumbling 



i ]>i.\\dT ea-ily. The fossil nacer gave 0.085 per cent, of 



ni.r , \\hili- fresh shells of the present jwriod frequently 



contain as mm-h as 0.14* |HT cent. Thus it can be definitely 



I that the 1'nionuhe in pre- Pliocene times were u>iii^ 



the < li -IIH ut manganese as we find them today. It seems pn>b- 



.iblr tliat tin marine ancestors of the l*nioniclu were thcmscKe- 



inan^.initi -r.-u-.. The fact that at least one marine lamelli- 



liran.h i- kii"\\n makes such an assumption the more plausible. 



I'., determine \\lu-ther mlu-r marine lamellibranchs utili/e 



inan^an.-M- in thi- same way, an examination of the common 



I. uni- aloni: the coast of southern Massachusetts was made at 



ih. \\ 1- Molt- laboratory. In several forms the elements 



could u-ualK l.e detected as a trace, but in such cases no import 

 (an be atta. hed to its presence except as indicating that then- 

 i- -oine marine low form of life serving as food for lamellibranchs, 

 \\hirh also . arries manganese. In Pectcn the man^am -< was 

 \ariaMe. -ometimes large in amount, at others very small. It 

 was frequently found abundant in the stomarh contents. In 

 nwtliolus the element was present in every specimen 



