[Reports volI-XIII] . aled in anyother age or region. As regards the distribution of the groupin time and space, and the phylogenetic history of the camerateforms in general, many pregnant suggestions have been offeredrecently by certain observations made in the Mississippi valley. More than three-fourths of the total number of the generaof the Actinocrinidse are represented in America, distributedin time as shown in the accompanying chart (plate xi)—therelative expansion of each genus being also indicated. As com-pared with the ages preceding, the lower Carboniferous is heregreatly exaggerate
[Reports volI-XIII] . aled in anyother age or region. As regards the distribution of the groupin time and space, and the phylogenetic history of the camerateforms in general, many pregnant suggestions have been offeredrecently by certain observations made in the Mississippi valley. More than three-fourths of the total number of the generaof the Actinocrinidse are represented in America, distributedin time as shown in the accompanying chart (plate xi)—therelative expansion of each genus being also indicated. As com-pared with the ages preceding, the lower Carboniferous is heregreatly exaggerated in order to show more clearly the relation-ships of the several zoological groups; for it was during thistime that the greatest diversity of form, structure and generalornamentation occurred ; in fact, it was the culmination of crin-oidal life in America. Continuous lines are drawn where therecord is complete and the transitions fully shown; while the MISSOURI GEOLOGICAL SURVEY. PLATE XI. f AMERICAN ACTINOCRINIIM;. DEVELOPMENT OF ACTINOCRINUS. ORINOIDS. 149 dotted lines indicate the relation of the different types accordingto the evidence at present known, and probably coincide veryclosely with the real courses of divergence. The scheme is,then, to represent in a graphic way the relationship of thegenera as now understood, rather than to construct a genealo-gical tree, with which attempts of this kind are often con-founded. In the present instance, some of the earlier, moregeneralized forms have not been made known as yet. Thereare also good grounds for believing that some of the generictypes are considerably older than actual observation other groups, more particularly, there is abundant evidencepointing to a much higher antiquity of the leading generictypes than is generally supposed. This is especially true ofmany widely distributed living organisms whose ancestry haslately proved to be very ancient. The most generalized type of the family Actinocrinidsehasdorsa
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