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and the Recent Echinid Faun. 41 
n comparing the genera characteristic of the Chalk with 
those now found living, we find that a considerable number of 
the latter date back to the Cretaceous period; and a few of the 
Cidaridx, the Echinide, the Salenide, the Echinoconide, and 
the Petalosticha, even to the earlier epochs, to the Jurassic beds, 
the Lias and the Trias. The genera Dorocidaris, Phyllacanthus, 
in 
the Tertiaries, in addition to the above genera, the following 
From our study of the embryonic stages of the Echinide, 
the Clypeastride, and the Spatangids, and a comparison of 
these stages with the genera of the Desmosticha and Petalos- 
ticha which have either succeeded the genera above mentioned, 
or have lived with them during the Cretaceous period and have 
oe time. But this connection is so complicated, and rami- 
; - in so many directions, that it must be hopeless, even with 
€ small number of species of Echinids known, to attempt to 
