68 GEOLOGICAL BIOLOGY. 



The "Hemera" of Buckman.* — Buckman has recently pro- 

 posed the term Jicmera {r/iAepa, a day) to indicate a time- 

 division of this nature. He writes: " The term * hemera * is 

 intended to mark the acme of development of one or more 

 species. It is designed as a chronological division, and will 

 not therefore replace the term ' zone ' or be a subdivision of 

 it, for that term is strictly a stratigraphical one. . . . 

 Successive ' hemerae ' should mark the smallest consecutive 

 divisions which the sequence of different species enables us to 

 separate in the maximum development of strata. In attenu- 

 ated strata the deposits belonging to successive hemerae may 

 not be absolutely distinguishable, yet the presence of succes- 

 sive hemerae may be recognized by their index species, or 

 some known contemporary ; and reference to the maximum 

 developments of strata will explain that the hemerae were not 

 contemporaneous, but consecutive." 



Again he writes: "Our present 'zones' give the false 

 impression that all the species of a zone are necessarily con- 

 temporaneous; but the work of Munier-Chalmos in Nor- 

 mandy, and my own labors in other fields, show that this is 

 an incorrect assumption. The term ' hemera ' will therefore 

 enable us to record our facts correctly ; and its chief use will 

 be in what I may call ' paLxo-biology.' " f 



The Terms Age of Reptiles, Planorbis Zone, etc. — The no- 

 menclature at present in use in geological classification, it 

 will be seen, is a nomenclature for the classification of forma- 

 tions, and is applied to the time-classification for want of a 

 better. We have in use names for a few of the grander di- 

 visions of time properly chosen, as the ages of man, of 

 mammals, of reptiles, etc., and in a few cases subdivisions 

 of the finer kind have received names after the same plan, as 

 the planorbis :;ojic and the angtilatns zone, before referred to 

 in the classification of the Ammonite beds of the Jurassi'c. 

 The selection of time-designations by this method can only 

 come through careful study of the characteristic fossils on the 



* S. S. Buckman, "The Bajocian of the Sherborne District: Its Relation 

 to Subjacent and Superjacent Strata": Q. J. G. S., vol. XLix. p. 481, November, 

 1893. 



\ L. c, p. 482. 



