Pakontological Speculations. — Gratacap. 233 
junction of favorable circumstances and exuberant vitality in 
this phylum occurred at that time. 
Dr. Carpenter in the "Voyage of the Challenger" has 
shown that while the stalked crinoids are partially abyssal 
they are not universally so, and if their abyssal habitat is to 
be interpreted as a retreat from shallower waters, we may be 
sure that the Lower Carboniferous seas were in no real sense 
abyssal. But it has been shown in the same work that the 
crinoids occur in groups, that if at any time they were con- 
tinuously found over the sea that continuity is interrupted. 
There is a strong probability that in the Lower Carboniferous 
seas there was no geographical continuity of crinoidal life, 
but that a group of basins existed which were characterized 
each by its special faunal development, and had their origin 
somehow in the survival of those genera which existed in the 
early palaeozoic, as Agelacriniis, Calceocrinus, Cyafhocriuns, 
Dorycrinns, Ichthyocrinus, Megisfocriniis, Mclocrinus, Platy- 
crinus, Poteriocrinns, Synhathocrimis. 
And for this reason — the crinoids of the whole palaeozoic 
are local, in distribution ; they form segregated fossils. The 
expression of the group derived from their occurrence is spor- 
adic, their habitat so to speak is concretionary. It can be ac- 
counted for by assuming that the character of the bottom is 
important in establishing their growth, that selection in this 
respect is decisive, and so, as the requisite foundations are 
limited, the crinoidal growth is limited and special. 
In the Trenton, in New York, the Caryocrinus is found. in 
small assemblages, and in the Cincinnatti beds locriniis and 
Dendrocrinns occur almost invariably in nests, groups, or bun- 
dles. In the Lower Helderberg Mariacrimis is also partial 
in its occurrence, and in the Waldron the Eucalyptocrinus, 
while more widely disseminated suggests colonies in its de- 
velopment. The Megistocriniis of the Upper Helderberg and 
Hamilton are uncommon, but when found are in bufiches, and 
the large crinoidal stems in these formations seem crowded in 
localized areas. 
The faunal basins we refer to in the Lower Carboniferous 
may have migrated, moved in and out, from the continent, up 
and down a coast line, but they became finally established 
in the Lower Carboniferous upon the most enduring basis. 
