68 GEOLOGICAL BIOLOGY. 



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

 posed the term hemera (r//jepa, 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 ' palaeo-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 zone and the angulatus zone, before referred to 

 in the classification of the Ammonite beds of the Jurassic. 

 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. 



f L. c., p. 482. 



