606 VICTOR E. SHELFORD 
9 Formations of the waters." 
a Formations of the sea (marine) (M’Intosh, ’04). 
Limestone bank formations (littoral) (Brooks, ’93). 
Rocky (eroding) shore formations (Littoral) (Verrill, 72; King and 
e Russell, ’09). 
Ne 
3 Sandy (depositing) shore formations (littoral). 
4 Open sea formations (pelagic) (Heilprin, ’81). 
5 Deep sea formation (mudline and abysmal). 
It should be noted that the various formations of the list are 
to be found duplicated or essentially so in various parts of the 
world. This point of view emphasizes the resemblances in the 
behavior and ecology of forms living under similar conditions. In 
the case of the great zoogeographic regions, there is no duplication, 
and differences are emphasized." 
13 The distribution of aquatic animals is governed by: a. Kind of bottom (Sum- 
ner, 09). b. Depth, current, temperature and all other factors which are modi- 
fied by depth, ete. 
14 There are no doubt several valid objections to such a classification, when thus 
statically stated and as mapped by some workers, such as Schimper. We present 
it thus because the recognition of the existence and general features of a phenomenon 
must precede its analysis. However, one of the most important of these objec- 
tions arises when one inspects a number of maps of the distribution of species. 
Such an inspection shows that the distribution areas of some species are bounded 
by the limits of the deserts, steppes, forests, etc., while those of others bear no 
relation to these regions. The former afford no difficulties while the latter deserve 
further comment. Species that, apparently, do not fit our classification fall under 
three heads: 1. Species whose range is far greater than that of any realm or plant 
formation, covering perhaps several realms. 2. Species that occupy only a part 
of the plant formation in which they belong. 3. Species whose range lies within 
a region intermediate between two realms or plant formations. 
The first group is made up of species dependent wholly or in part upon local 
conditions. Some species are always associated with local conditions, e.g., C. 
tranquebarica, p. 574, fig. 14. Such forms are relatively independent of climate, 
geographic plant formations, etc., and are dependent upon such conditions as 
are afforded by streams, sand areas, lakes, etc. ; 
The species which are in part dependent upon local conditions usually belong 
properly to the climatic or geographic conditions of one formation, and invade 
another formation in local conditions which happen to be like the geographic of 
the one, in respects essential to that species. For example, some of the species 
of Orthoptera belonging to the great plains, or North American steppe region, in- 
vade the sand areas in northern Indiana where the climate is suitable for forests. 
Such phenomena are common and have been discussed by Adams (’02, 09). 
