NO. 6 MIDDLE CAMBRIAN BRANCHIOPODA, ETC. 1 53 



Heldensis, and Naraoia compacta are of more or less frequent 

 occurrence. 



Layer No. lo gave many beautiful specimens, including several 

 fine sponges and sertularians. Of the annelids, Ottoia proliUca, 0. 

 minor, Selkirkia major, S. gracilis, Oesia disjuncta, Polling.eria 

 gracilis, Wiwaxia corrugata, W orthenella cambria, Asheaia pedun- 

 culata, Canadia spinosa, and C. setigera are present, and among the 

 holothurians, Laggania cambria, Mackenzia costalis, and Louisella 

 pedimculaia. The medusa Pcytoia nathorsti also appeared at this 

 horizon. The crustaceans include Marrella, Burgessia, Waptia, 

 Nathorstia transitans, Naraoia compacta, Bidentia diMcilis, Emerald- 

 clla brocki, Leanchoilia stiperlata, Hymenocaris perfccta, H. obliqiia, 

 H. ? circularis, H. ovalis, H. ? parva, Tuzoia retifera Fieldia lanceo- 

 lata, Hurdia victoria, H. triangulata, and Odaraia alata. Among 

 the trilobites Neolenus serratus is found with its antennae, caudal 

 rami, branchiae, and legs finely preserved. 



No. 8 gave many plates of the annelid P olling^eria 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 abun- 

 dant over a limited area, and also Marrella splendens and Hymeno- 

 caris perfecta. 



Above No. 5 the scattered valves of Hymenocaris perfecta and 

 more or less imperfect annelids (Ottoia proliiica, Pollingeria grandis, 

 and BantHa grandis) were occasionally found, along with sponges, 

 brachiopods, and fragments of trilobites. The small gastropod 

 Scenella various 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. 



CLASSIFICATION 

 The classification used is partly that of Dr. W. T. Caiman as out- 

 lined in Lankester's Treatise on Zoology, 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. 



