82 The American Ceoloj^ist. ivi-nmry. v.m. 
Of course this is a general proposition. Selection might 
rapidl}'^ augment the growth of hard parts in some sections of 
animal life, and comparative immunity from attack or injury, 
retard or but laboriously develop them in others. There 
seems no advantage in either size or mass except so far as 
one or the other, or both, enable an animal to resist destruction 
or in predatory examples, chase its prey. 
The impression, very quickly and keenly felt in examining 
Cambrian fossils, is that they are small and thin. The trilobites 
remain conspicuously contrasted with their associated fauna^ 
and suggestions are also evident that the worms may have been 
large. The morphological impulse which produced large trilo- 
bites and worms and left everything else small is not without 
interesting suggestions, especially as the largest and strongest 
examples are Middle or Lower Cambrian. 
But primarily, is it true that Cambrian life exhibits diminu- 
tive and fragile forms? It certainly seems to. There are na 
large brachiopods, no corals of appreciable size, no large lamel- 
libranchs. no crinoids, few and insignificant univalves. The 
character of the fauna in these respects is provisional and in- 
troductory. The examples of Brachiopoda belong mainly to 
the inarticulate group wherein functional organization is high, 
but the later secretatory activities, those which made shells,, 
loops, teeth, etc., which became excited and specialized under 
new conditions or accidents, were yet dormant. Dr. Walcott,. 
in his "Fauna of the Lower Cambrian or Olenellus Zone," has 
furnished a review and exposition of what is known of the 
fauna of this early age. It presents a scattered and broken out- 
line, as from the circumstances was inevitable, of the inverte- 
brate forms of life. It can be, as far as research has gone,, 
neither full nor complete. The forms of life are small and 
feeble. The trilobites alone, and the worms, present evidences 
of abundance and development and strength. 
In the Hall cabinet Lingulepis pinniformis, Oholella polita, 
LingiileUa mosia, L. aurora, L. stoneana, in the western Pots- 
dam are numerous and indicate zones or areas of successful 
multiplication. In the Troy limestone beds Lingulepis mini- 
ma, L antiqua, and Oholella prima seem also plentiful. The 
trilobites present in the western sandstones the familiar feature 
of great numbers. The annelidan indications arc necessarily 
