JRenew-i — Dr. C. Davison — Origin of Earthquakes. 377 



stock as Apics. We see the commencement of the' Trilobite form in 

 Marrella, an ^^ws-like Crustacean, but more highly developed, and 

 with jointed legs and fewer segments. Marrella, with its leg-like 

 endopodite and expanded gill-like epipodite, is very abundant in the 

 Burgess Shale, and has a small, strong, sub-quadrangular carapace 

 with two postero-lateral spines and sessile eyes. 



The Cambrian Crustacean fauna seems to show that five main 

 stems (Branchiopoda, Malacostraca, Ostracoda, Trilobita, and Mero- 

 storaata) started in the early Cambrian, and that all had their 

 beginning in pre-Cambrian (Lipalian) time. Dr. Walcott thinks 

 that more work in the Lower Cambrian will bring to light a large 

 and varied Crustacean fauna : the occurrence of Beltina in the pre- 

 Cambrian of the Eocky Mountains certainly seems to support this. 



In dealing with the descent of the Cambrian Crustaceans from a 

 "theoretical ancestral stock" (correlated with the Apodidse) the 

 author assumes that the Branchiopoda came first, and from these 

 three distinct branches were developed before or during the Cambrian. 

 The Trilobites are thought to come directly from the Branchiopods, 

 and descent is considered to go through the Aglaspina and Limulava 

 to the Eurypterids, and thence to the Xiphosura. The Hymenocarina 

 and the Ostracoda are the other two lines of descent from the 

 Branchiopods. These views are regarded only as tentative, and 

 Dr. Walcott hopes to make a more detailed study when further 

 material is available. The eleven plates illustrating this paper are 

 particularly fine. 



jJ^o. 8 (publication 2076) of the same volume of Smithsonian 

 publications is a paper by the same author on " The Sardinian 

 Cambrian genus Olenopsis in America ". Until now the stratigraphical 

 position of this genus in relation to the Olenellus and Paradoxides 

 faunas has been uncertain. In the present paper Dr. Walcott describes 

 three new species {0. {?) agnese^isis, 0. mnericanus, and 0. roddyi) 

 which give the genus a definite horizon and an extensive geographical 

 range in jS^orth America, the new localities being in Central Penn- 

 sylvania, Montana, Alberta, and British Columbia. The horizons 

 are Lower Cambrian and the passage beds to the Middle Cambrian. 

 From the evidence Dr. Walcott suggests that the genotype — 0. %oppii 

 (Meneghini) — occurs beneath the Middle Cambrian Paradoxides beds 

 in Sardinia, and as regards generic relationships he thinks that both 

 Olenopsis and Paradoxides are descended from the Solmia type of the 

 Mesodonacidse. There is one plate, and this contains, besides figures 

 of the new species, several photographs of 0. zoppii from the type 

 locality for comparison. 



III. — The Origin of Earthquakes. By Charles Davison, Sc.D., 



E.G.S. 8vo ; pp. viii, 144, with 26 text-illustrations. Cambridge: 



at the University Press, 1912. Price ls.net. 



rPHIS is a companion volume to that on Rocks by Professor Cole, 



1 and gives a comprehensive view of what is known about the 



origin of Earthquakes in language clear and concise. The author's 



plan is to confine his attention to the phenomena essential to any 



