242 SCIENCE PROGRESS 



author's observations on the osteology of the genus are valu- 

 able, but we note that he ignores the proposals of the American 

 Committee on the nomenclature of the cranial elements of the 

 Reptilia. The findings of that Committee, which were eminently 

 sound, were published by the Geological Society of America 

 in 191 7. 



In a short paper on the significance of the divergence of 

 the first digit in the primitive mammalian foot, Mr. J. W. 

 Gidley has contrived to raise some interesting and im- 

 portant points (Journ. of the Washington Academy of Sciences, 

 vol. ix). He comes to the conclusion that the primitive 

 mammalian foot must have been primarily terrestrial, and 

 that from this generalised type of foot, with divergent but not 

 primarily opposable first digit, have been developed all sorts 

 of modifications of foot structure. The divergence of the first 

 digit, he considers, is primarily an inheritance from the primi- 

 tive reptilian condition, and cannot be considered as in any 

 way supporting the hypothesis of an arboreal ancestry of the 

 mammalia. 



Finally, mention must be made of the memoir on the 

 Appendages of Trilobites, by Prof. C. D. Walcott (Smithsonian 

 Miscellaneous Collections, vol. lxvii, No. 4). For more than 

 forty-five years the author has been working on this theme. 

 He now publishes the notes and illustrations he has accumu- 

 lated since 1894, and these will meet with the appreciation 

 they deserve, not only by palaeontologists, but students of 

 living Crustacea, for the author not only commands an un- 

 rivalled knowledge of his subject, but he has had the further 

 advantage of exceptionally fine material to work upon. 



