No. 10. — The Trilobite: New and Old Evidence relating to its 
Organization. By ©. D. WALCOTT. 
INTRODUCTION. 
Ters publication terminates, for the present, an investigation that 
has occupied much time and attention during the past seven years. 
In the month of October, 1873, the attention of Professor Louis Agas- 
siz was called to certain markings on the inner side of the pleure of a 
specimen of Asaphus platycephalus, “ Panderian Organs.” He con- 
sidered them as proving the existence of true crustacean legs. (Amer. 
Nat., VII. 741, 1873.) With his characteristic liberality Prof. Agassiz 
offered facilities for study, and strongly urged that an attempt should 
be made to discover the ventral surface of the animal and the character 
of the attached appendages. It affords me pleasure to state here that 
whatever there may be of value in this contribution to our knowledge 
of the subject is owing largely to the spirit of investigation that he 
awoke and which has carried forward the work under many adverse 
circumstances long since his death. 
The prosecution of the investigation during the year 1874 gave 
the material from which the notes on the inferior or ventral surface of 
the dorsal shell of Ceraurus pleurezanthemus were written. Judging 
from the dorsal shell alone the views of Burmeister were given as best 
explaining the facts then known.* 
The succeeding year thin sections of Trilobites were cut from both 
Lower and Upper Silurian rocks. In the upper portion of the Trenton 
limestone at Trenton Falls, N. Y., a thin layer of dark, bluish-gray, 
fine-grained, partially impure limestone was found, that contained 
many very perfectly preserved trilobitic remains. On examination of 
these by cutting sections, it was ascertained that other parts of the 
animal besides the dorsal shell and hypostoma were present. Specimens 
from all other localities and formations failed to afford more than the 
strong dorsal shell and hypostoma. This fact once established led to 
the extended working of the prolific stratum. The soil and rock to a 
depth of nine feet was removed, over a large area, to obtain the fos- 
sils scattered through the thin layer of limestone. From this area 
* Ann, Lyceum Nat. Hist. of New York, XI. pp. 155-162, 1875. 
VOL. VIII. —NO. 10. 
