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NEW YORK STATE MUSEUM 



which approach closer to the usual expression of the Hamilton 

 species below, and from a gradation between the dwarfs and 

 the normal Hamilton forms. As these species are unquestion- 

 ably immediately descended from Hamilton ancestors, they are 

 here considered as variations from the normal Hamilton species, 

 and are described as mutations. This term is used not only in 

 the common acceptance of the word, but within the meaning is 

 incorporated the conception that the species have arisen under 

 abnormal conditions. This seems to me preferable to calling 

 them new species, though the variation is considerable in many 

 cases. The resultant forms are such as might have arisen from 

 a laboratory experiment. On considering the small size and the 

 simple ornamentation of the specimens, the first suggestion is 

 that they are young. But a whole fauna can not exist of im- 

 mature forms alone. There is further a uniformity in the size 

 of the individuals of each species, which can only express adult 

 growth. The Goniatites indicate this with clearness ; here are over 

 100 representatives, all apparently of one species, each a per- 

 fect miniature Goniatites with three whorls and 25 or more cham- 

 bers, the whole no larger than the primitive three whorls of 

 the normal species of Goniatites, from which they are evidently 

 derived. The Brachiopoda specially show uniformity in the 

 development of size; a valve with 10 or 11 ridges and furrows, 

 with septum, muscular impressions and several lines of growth, 

 will not be more than two or three times as large as the pro- 

 tegulum of the same species from the Hamilton. The specimens 

 are nevertheless essentially adults, so far as their relation to 

 the congeries as a whole is concerned, though having usually 

 only about one fifteenth the diameter of +heir progenitors. 



The fauna is not uniformly dwarfed, large specimens occa- 

 sionally occuring among the otherwise tiny forms. Some groups 

 of species are more affected than others. The dwarfing agent 

 has totally eliminated the corals; the Brachiopoda are most uni- 

 formly and extensively dwarfed; the Lamellibiam hiata are much 

 affected; the Gastropoda and Cephalopoda are mostly tiny, but 

 also have some medium and occasionally large sized represenla- 

 tives, all adults. 



