Early 'Trilobites of the Cambrian (Rocks — Matthew. 9 
The last named genus exceeds all the others in the develop- 
ment of the thorax, both in the number of the joints and in the 
mobility of the segments. And corresponding to this is the 
great development of the movable cheeks and genal spines. 
The Paradoxides of the Acadian series are remarkable for 
the large number of species with continuous eyelobes; this fea- 
ture is more marked in the early larval forms than at later 
stages in the life of the trilobite, and is an embryonic character 
which is more prevalent among the species which first appeared 
than in those which existed in the closing period of the reign 
of the Paradoxides. The eyelobe in the early stages of growth 
in this genus was separated from the anterior margin by abroad 
flat area, which in later stages was considerably narrowed at 
the front. But in the Ptychoparinae the relative changes in 
these parts were quite the reverse of this; for counting the 
ocular fillet in this sub-family as analogous to the front of the 
palpebral lobe in Paradoxides, the space between it and the 
anterior margin became continually wider as the trilobite grew. 
The following are the species which in Europe most nearly 
represent the Acadian forms of this genus: 
European. Acadian. 
Ififl^'rhtrEsi?} Paradoxides acadieus. • 
P. olandicus. P. lamellatus. 
P. rugulosus. P. eteminicus. 
P. ■: palpebrosus. P. micmac. 
P- brachyrachis.1 p nnntifipilis 
P. hicksii? i ^- pontiticaiis. 
P- forehammeri?) p ,.p£?ina 
P. spinosus? / ^- legma. 
P. tessini. P. abenacus. 
There are many points of interest relating to the early life of 
the Cambrian age that have not been touched upon in the above 
remarks, but to detail them here would swell this paper to un- 
necessary proportions. Sufiicient has been said to show how 
replete with interest to the biologist is the threshold of palaeo- 
zoic life and how nearly the development of the early Cambrian 
faunas corresponded on the two sides of the Atlantic.' 
