246 STALK-EYED CRUSTACEA. 
on the coast of Florida extend from a few fathoms off shore to 2000 fathoms. 
Considerations like these will put one on his guard against such an assump- 
tion as that above alluded to. Pourtalés was surprised at the bulk and 
massive type of the West Indian Tertiary simple corals as compared with 
their modern representatives which he dredged in the Caribbean Sea. But 
this difference is explicable if we suppose that the ancient forms were littoral. 
Under the enormous pressure which exists in deep water, great size is pos- 
sible only when accompanied by a soft and freely permeable texture. The 
calcareous shells and corals from deep water are generally small, or if large, 
extremely thin and fragile. The deep-sea Crustacea, as a rule, lack the 
rigid caleareous coat which protects their littoral relatives. Species living 
under a pressure of a ton or more to the square inch are often so limp and 
delicate that it is difficult to secure a perfect specimen. By casting away 
their armor, their battle with the abyss was won. 
The small number of ancient types of Crustacea preserved in the great 
depths of the ocean is not a subject for wonder if we bear in mind the fact 
that most of the fossil Crustacea known to us are probably littoral, or from 
the present point of view, shallow-water forms. The changes in environ- 
ment to be met and overcome by a highly specialized littoral species in 
adapting itself to life at great depths are presumably as great, and lead to as 
much structural modification as those encountered by the littoral descend- 
ants of ancient species through the vicissitudes of the shores. As a concrete 
example, I will instance the family Galateida. This family has a very 
extensive vertical distribution, being represented at all depths from the 
littoral zone to below 2000 fathoms. But this great distance is apportioned 
in a rough way among the different genera of the family. In the shallower 
waters from the shore to 25 fathoms the genus Galatea prevails, in the 
deeper, but not abyssal belt Munida comes to the front, while in the greater 
depths below 500 fathoms the family is represented chiefly by the blind 
genera Galacantha and Munidopsis. Now MM. Milne Edwards and Bouvier * 
have shown, in their interesting memoir on this group, that as we pass from 
the shallow-water Galatea, through M/unida, to the deep-sea genera Galacan- 
tha and Munidopsis, we depart further and further from the more primitive, 
generalized, or Macruran type. 
In some instances the more primitive types of Crustacea flourish in the 
* Considérations Générales sur la Famille des Galathéidés. Par MM. A. Milne Edwards et HE. L. 
Bouvier. Ann. Sci. Nat., Zool., 7¢™° Sér., XVI. 315-317, 1894. 
