Page:Proceedings of the United States National Museum, Volume 76.djvu/133

Rh definitely indicated, but since the lower part of the Burton formation outcropping nearby apparently contains a fauna of similar age, while the upper portion contains the Middle Cambrian Albertella fauna, it becomes apparent that here the upper Mount Whyte, (Kochiella fauna), is absent.

The rare Pennsylvania fossils herein described or referred to are all in the Kinzers formation, which has the typical Mesonacid fauna that is comparable with the Eager formation just mentioned. Beside the Tuzoia, Anomalocaris, and merostome described from this formation in this paper several other unusual fossils have been found, including notably a sponge and a species of some Holothurian possibly belonging to the genus Peytonia. Both the eastern and western Mesonacid faunas have now furnished such fossils that clearly show that the Burgess shale fauna was derived from the same ocean.

Several other Lower Cambrian collections from western North America, made in fine grained argillaceous rocks that break with sufficiently large smooth surfaces to preserve them, give us specimens of phyllopods, among which such genera as Hurdia, Hymenocaris, Isoyxs, together with several new ones, are represented or suggested. In eastern Yun-nan, southern China, Mansuy has found several phyllopods in the Redlichia beds, quite similar to those from the western American Mesonacis bearing beds, and in addition a merostome that he described as Amiella prisca. Thus it will be seen that many of the "lower" crustacea as well as algae, sponges, jellyfish, and worms were already important in the Lower Cambrian seas, and if we should ever be so fortunate as to find another Burgess shale preservation in these older rocks we may expect a great array of organisms. It will also be observed that indications point to the direct descent of the Burgess shale fauna from these older Mesonacid assemblages. It might be added that certain trilobites in the Eager beds seem to belong somewhere between the Mesonacidae and such Middle Cambrian forms as Zacanthoides.

All the faunas here discussed, both the Lower and Middle Cambrian, lived in epicontinental seas whose waters were apparently extensions of the Arctic Ocean.

Knowing very little about the structure and systematic relations of the crustacea, I hesitate to say anything in this connection regarding the biological significance or relationships of the fossils presented in this paper, but a few general observations may be in order.