Page:Walcott Cambrian Geology and Paleontology II.djvu/235

 fieldensis, and Naraoia compacta are of more or less frequent occurrence.

Layer No. 10 gave many beautiful specimens, including several fine sponges and sertularians. Of the annelids, Ottoia prolifica, O. minor, Selkirkia major, S. gracilis, Oesia disjuncta, Pollingeria gracilis, Wiwaxia corrugata, Worthenella cambria, Asheaia pedunculata, Canadia spinosa, and C. setigera are present, and among the holothurians, Laggania cambria, Mackenzia costalis, and Louisella pedunculata. The medusa Pcytoia nathorsti also appeared at this horizon. The crustaceans include Marrella, Burgessia, Waptia, Nathorstia transitans, Naraoia compacta, Bidentia diMcilis, Emeraldella brocki, Leanchoilia superlata, Hymenocaris perfecta, H. obliqua, H. ? circularis, H. ovalis, H. ? parva, Tuzoia retifera Fieldia lanceolata, Hurdia victoria, H. triangulata, and Odaraia alata. Among the trilobites Neolenus serratus is found with its antennæ, caudal rami, branchiæ, and legs finely preserved.

No. 8 gave many plates of the annelid Pollingeria grandis and several specimens of the large Odaraia alata. In the dirty-gray layer of No. 9 the large Anomalocaris gigantea occurred.

In layer No. 5 the pelagic holothurian Eldonia ludwigi was abundant over a limited area, and also Marrella splendens and Hymenocaris perfecta.

Above No. 5 the scattered valves of Hymenocaris perfecta and more or less imperfect annelids (Ottoia prolifica, Pollingeria grandis, and Banffia grandis) were occasionally found, along with sponges, brachiopods, and fragments of trilobites. The small gastropod Scenella varians is found throughout the phyllopod bed and often its depressed conical shell, with the apex up, occurs in great numbers.

The mode of occurrence and limited area of the fauna indicate that we have only a portion of a crustacean fauna that was already developed early in Cambrian time and whose descendants swarmed in the Silurian and Devonian seas.

The classification used is partly that of Dr. W. T. Calman as outlined in Lankester's Treatise on Zoölogy, Part VII, 1909, and such additions as I have found it necessary to make in describing the many unique forms from the Burgess shale. All of the genera described in this paper fall under the subclasses Branchiopoda, Malacostraca, Trilobita, and Merostomata, and existing orders.