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1878. ] Walks Round San Francisco, 791 
borne on stalks, and very conspicuous antenne and mouth appen- 
dages. Thus he belongs to the Decapoda or ten-footed crustacea, 
while the other sand- hoppers, with seven pairs of limbs and sessile 
eyes, are in a lower sub-class. His great forte appears to be dig- 
ging in the sand, which he does backwards, and with astonishing 
rapidity, disappearing in an attitude similar to that of a diving 
uck. Securing a few of these lively fellows, we return up the 
watercourse and across the sandy prairie to the road, gathering, 
as we proceed, a few flowering stalks of the yellow Bahia lanata 
and a twig of Croton procumbens, with its light green berries. 
I think it is about time that the notion that a species must 
necessarily be named after some peculiarity that it possesses, 
should pass into the limbo of exploded ideas. There are now so 
many species of animals known, that it is, in many cases, impos- 
sible to define the differences between those which are nearly 
related in one word—it needs at least five lines of writing to do 
it. Two species differing in twenty particulars, no one of them, 
perhaps, very important, cannot be correctly distinguished by 
incorporating one of these points of difference in a specific 
name, and it frequently happens that a name which correctly 
describes one species will apply equally well to another species 
which has other peculiarities rendering it totally different. Thus 
Sebastes ruber, the red rock cod, is red enough, but there are two 
or three other red species of the same genus in our waters; and 
among the shrimps of the genus Hippolyte, H. brevirostris, 
although it has a short rostrum, is excelled in that particular by 
other species. As species are distinguished from each other not 
by one but by several peculiarities, it sometimes happens that the 
very character which, from its conspicuousness, has been incor- 
porated into the specific name, may be wanting in an individual 
which yet belongs to the species; thus Astertas ochracea, the 
ochreous star-fish (our common species), is quite as frequently 
` deep purple as yellow, and Astacus nigrescens, the blackish cray- 
fish, is usually of quite a light tint. ~ 
The great necessity of zodlogical and botanical nomenclature 
is not so much to have a descriptive name for every species as to 
have one fixed, indisputable name by which each shall be univer- 
sally known. This is an end difficult to reach, but will, at least 
in the majority of cases, be at length attained. Isolated workers 
in different countries, or distant parts of the same country, not 
