Ciassllicat'ion of the Biuirliiojxxia. — SfKnehr-rt. 14 7 
ception in the Lower Silurian, hut are not a pronounced paleozoic 
group. However, on reaching the Jurassic and Cretaceous, the 
rocks fairl}^ abound with their shells, and from that time on they 
are the chief representatives of the class. Lingnla and Cninla 
are present in the Lower Silurian, and as far as can be determined 
have persisted to the present time. 
The Atremotti, which contains the oldest and the simplest 
forms structurall}', is represented b}' twenty-four genera, while 
the NeotreitKitd and Protreniatu originating almost simul- 
taneously from the former have thirty-one and eighty-two, re- 
spectively. The Telotremdia had its origin in the Neotremata. 
It is the last order to appear, and has by far the greatest number 
of genera, one hundred and thirty-eight. 
To Dr. C. K. Beecher the writer is indebted for many valuable 
suggestions, as well as for the careful reading of the manuscript 
of this paper. « 
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