Hyatt.] 236 [December 16, 



the TJte Indians, who occupy the western half of Colorado. 

 After referring briefly to the traditions current among them 

 respecting the origin of their tribe, he spoke of their recent 

 rapid decrease in numbers through the ravages of the small 

 pox. They still, however, maintain a tribal existence and a 

 certain degree of organization. He then described their 

 ways of living and domestic customs, referring to their bur- 

 ial rites and marriage contracts, and gave such information 

 as he had been able to obtain respecting their religious ideas. 



The following papers were read : — 



Abstract of a Memoir on the "Biological Belations of 

 the Jurassic Ammonites." By Prof. A. Hyatt. 



The speaker traced the history of the evolution of the order of 

 Ammonoids, showing that the characteristics of the first three stages 

 of the embryo were inherited from a very early period. These were 

 first, the sac-like shell of the embryo containing the equally sac-like 

 beginning of the siphon, — prosiphon as it has since been called byM. 

 Munier-Chalmas; second, the beginning of the true shell or apex, 

 with its nautilus-like septum, and peculiar nautilus-like umbilicus; 

 third, the depressed and goniatite-like continuation of the form of 

 the shell with its accompanying goniatitic septa. 



These of course represent only their most advanced stage in the 

 Ammonites proper of the Jura and Trias ; they are, when first ob- 

 served in the Silurian and Devonian, exceedingly variable in the 

 length of the periods and other important characteristics even be- 

 tween the varieties of different species. They become invariable in 

 the young as embryonic characteristics only after the lapse of time 

 represented by the Silurian, Devonian, and Carboniferous periods. 

 This variability in the same species in the Silurian shows how re- 

 cently they were inherited, and their invariability in every individual 

 of the Jurassic shows the result of the long ages of inheritance 

 through which the group has passed between that period and the 

 Silurian epoch. 



He then showed that in each subordinate group there were cer- 

 tain invariably occurring forms precisely similar to those found in 

 other groups often widely removed in time and very distinct in the 



