248 A HISTORY OF RECENT CRUSTACEA 
Leach, was at one time called Anchistia migratoria by 
Heller. But it differs from Dana’s Anchistia by having 
three flagella instead of only two on the first antennez, and 
by having the two spines of the carapace one above in- 
stead of one behind the other. Heller therefore instituted 
for it in 1869 the new genus Palcemonetes, which agrees 
with Anchistia but differs from Palemon in having no 
‘palp’ tothe mandibles. The development and larval me- 
tamorphoses of Palemonetes varians have formed the sub- 
ject of important studies by Dr. Boas, Mr. W. Faxon, and 
Dr. Paul Mayer. Its distribution has been summed up by 
Professor Th. Barrois. The same genus includes also the 
American fresh-water species, Palemonetes exilipes, Stimp- 
son, and Palemonetes vulgaris (Say), which appears like 
varians to be almost equally at home in salt water and 
fresh. It affords an abundant supply of food to many of 
the fishes on the east coast of the United States, and is in 
turn itself supported with equal liberality by other animals. 
Messrs. Verrill and Smith, after speaking of its inhabiting 
the brackish pcols and ditches, even where the water is 
but little salt, remark that it ‘also occurs in immense 
numbers on the muddy bottoms and among the eel-grass of 
the estuaries. In the pools there are also myriads of small 
Entomostraca of many kinds, upon which the prawn and 
other species feed,while the Entomostraca find an abundance 
of ciliated Infusoria and other microscopic animals for 
food.’ In regard to Paleemonetes varians an observation, 
perhaps generally applicable, was made by Hensen and 
confirmed by P. Mayer, that specimens in confinement will 
speedily shed their skins if well fed. The same authors 
showed also by very conclusive experiments that the 
animals after exuviation introduce fresh otoliths into the 
ear-cavity of the first antennz. Dr. Mayer supplied 
crystallised silver, and had the satisfaction of seeing a 
bright scale of this metal in one ear of his young Pale- 
monetes. Hensen points out that the introduction of 
otoliths must as a rule take place while the softness of the 
new skin permits the narrow opening into the ear-chamber 
to be stretched to the utmost limit. 
