146 Report op the State Geologist. 



similar. Examples abound in actual nature. Palaeontologists 

 have resolutely entered on this path and the results they have 

 obtained are most interesting. 



The first works in which large numbers of individual specimens 

 were brought under notice are those of Hilgendorf and of 

 "Waagen. The former of these writers'^ took up the study of the 

 minute shells belonging to the genus Planorhis^ which are found 

 by myriads at various horizons in the calcareous rocks of the 

 Upper Miocene of Steinheim (Wtirtemburg). These shells pre- 

 sent forms so varied that they seem entitled to be classed in 

 different genera. They are smooth, carinated, umbilicated, 

 turriculated, rounded, furrowed, etc., etc. Bronn had united 

 them all under the name of Paludina multiformis. Hilgendorf 

 and, followiDg him, Hyatt discoveredall the transitions between 

 the diverse forms and assert that they were derived one from 

 another. It must, however, be stated that these two writers did 

 not group them in the same manner. 



Not less important is the memoir of Waagen on ''The Series 

 of Forms of Ammonites suhradiatus.'^^ The author here describes 

 a great number of related forms which he groups under the 

 generic name of Oppelia, and he calls attention to an import- 

 ant distinction not hitherto remarked. The variations of one of 

 these forms are of two kinds. The one kind extend from one 

 locality to another in deposits of the same age; Waagen calls 

 these variations. The. other kind make their appearance in 

 successive deposits of the same locality ; he calls these mutations. 

 In describing diverse species, Waagen establishes the filiation of 

 all these species in time, and their variations according to 

 localities. 



As a third example of classification, we m.ay cite the history 

 of the Paludinas of the Upper Miocene, studied by ]^eumayr,f 

 to which we shall have occasion to again refer. 



These works were a point of departure for a marked reaction 

 against the former tendency, which was to multiply illimitably 

 the number of species. If many scientists still persist in over- 

 loading scientific nomenclature with a multiplicity of specific 

 denominations difficult of practical appjication, the greater num- 



* Monatsber. Berl. Akad.. 1866. 



+ NeumajT und Paul, Die Congerien unci Paludinen-Schichten Westslavoniens. {Ahhandl. Geolog. 

 ReichsansT., VII.) 



