1895.] The First Fauna of the Earth. 983 
Middle and Upper, are each characterized by a special genus 
of trilobite. Inthe lower zone we have Olenellus, in the middle 
zone Paradoxides, and in the upper zone Dikellocephalus. These 
three genera are so closely related that it does not require any 
stretch of the imagination to regard one as a descendant of 
the previously existing form. It is true there are no exactly 
connecting links between the three, and yet there are genera 
known which have certain intermediate characters. In some 
localities the three zones present an almost conformable se- 
quence, with scarcely a break in sedimentation, but in other 
places there is a very perceptible time interval between them. 
In the former cases, the intermediate genera are known to 
occur. 
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Fig. 10. Pteropoda (//yo/ithes). Fig. 11. Protocaris marshit. 
We have already seen that the fossils of the Lower Cambrian 
are found in New York, Vermont, New Brunswick, Newfound- 
