732 
PALEONTOLOGY: C. SCHUCHERT 
streams into the lagoon. If so, this is evidence of fresh-water life as 
far back as the Lower Cambrian. Further, in the uppermost Cam- 
brian at one locality in Wisconsin the present writer has collected a 
few fragments and one entire specimen of the ancient limulid Aglaspis 
in association with an abundance of trilobites, fragmented and entire, 
and many well preserved brachiopods (Westonia stoneana). In all later 
Paleozoic deposits the Hmulids are almost always associated with euryp- 
terids, and practically never in normal marine faunas. They are al- 
ways very rare fossils until early Pennsylvanian time, when Euproops 
dancE is common in that most interesting mixed estuarine and terrestrial 
fauna preserved in the nodules of Mazon Creek, Illinois. The Triassic 
limulids also appear to have Hved in fresh water, but since late Jurassic 
time Limulus has been in the sea, and is represented today by several 
living species in the Atlantic and Pacific oceans. Can, therefore, the 
annual return of these animals to the land to lay their eggs be a surviv- 
ing instinct and an ontogenetic expression of their earHer, fresh-water 
habitat? 
In this connection should be recorded a most interesting observation 
of Limulus made by Professor Barrell many years ago. He took home 
in the spring of the year a large female Limulus that he had picked up 
on the shore of New Haven Bay, and kept it in the grassed yard back 
of the house in which he lived. Under these conditions the animal 
was still able to crawl about feebly for two days and gave evidence of 
life for about a week, during all of which time it was out of the water. 
This clearly indicates that the gill-books are fairly easily adaptable 
to air-breathing, and the question may be asked whether in the Paleo- 
zoic during times of drought ancestral limulids of the fresh waters may 
not have lived over the dry season, as do the lung fishes of today, buried 
in the mud and breathing the air. 
Attention should also be directed to the occurrences of the Apus-like 
branchiopods, the oldest of which is Protocaris of the Lower Cambrian, 
known in a single specimen associated with trilobites in a marine deposit 
laid down, however, near the shore. In the Middle Cambrian black 
shale lagoon deposits (Burgess), there are three genera, and then we 
have no record of them again until Apus is met with in the Triassic — 
henceforth a persistent synthetic genus, which in the living world is 
restricted to the more or less evanescent land waters of many continents. 
If the eurypterids and limulids arose in the fresh waters, as appears 
probable, we can then the more readily explain why they and the ter- 
restrial scorpions do not pass through a crustacean naupHus stage, for 
they had to adapt themselves to the lands or to waters limited in dis- 
