Reviews 



"Middle Cambrian Merostomata." By Charles D. Walcott. 



Cambrian Geology and Paleontology, II, No. 2. 

 ' 'Middle Cambrian Holothurians and Medusae." By Charles D. 



Walcott. Ibid., No. 3. 

 "Middle Cambrian Annelids." By Charles D. Walcott. Ibid., 



No. s- 



In these three papers Dr. Walcott has described a portion of one of 

 the most remarkable extinct faunas which any paleontologist has ever 

 brought to light. The fossils occur in the Burgess shale of the Stephen 

 formation, in British Columbia. Their manner of preservation is un- 

 usual, the organisms being pressed flat, the soft-bodied Holothurians 

 Medusae, and Annelids being represented only by thin films which 

 fortunately are darker than the shale and are usually shiny. The 

 internal structures are often preserved in glistening, silvery surfaces, 

 even to the fine details. The illustrations of the fossils have been 

 beautifully executed by an ingenious process of photography by reflected 

 light, the photographs being reproduced upon heliotype and half-tone 

 plates. 



The Merostomata contained in this remarkable fauna are referred 

 to two new genera, Sidneyia and Amiella, both included in the order 

 Eurypterida, and each made the type of a new family. Each genus is 

 represented by a single species. Sidneyia inexpectans is a remarkable 

 type, such as might be expected in an Ordovician rather than in a Middle 

 Cambrian fauna, it is much the commoner of the two and some of the 

 specimens are preserved in such a perfect condition that the structural 

 details of the ventral appendages, even of the branchiae, can be worked 

 out. Amiella ornata is represented in the collection by a single broken 

 specimen, and is consequently much less perfectly understood. 



The commonest of the Holothurians, Eldonia ludwigi, a new genus 

 and species, is a peculiar, free-swimming type, with an umbrella-shaped, 

 medusa-like body, growing to a size of 12 cm. in diameter. The spiral 

 alimentary canal, the oral aperture and tentacles, and the water- 

 vascular system are well shown in many of the specimens. Other Holo- 

 thurians with more or less elongate, cylindrical bodies, having more the 

 form of living members of the class, are represented by the new genera 

 Laggania, Louisella, and Mackenzia. The Medusae are much less 



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