1905.] NATURAL SCIENCES OF PHILADELPHIA. 693 



quite within the range of elegans, which sometimes has nineteen, and 

 occasionally seventeen rows; and as in the remaining details of scutella- 

 tion, as well as in other characters distinctive of elegans, such as the 

 yellow chin and throat, the usually short hinder chin-shields, and the 

 frequent presence of red markings on the ventrals, there is complete 

 agreement, it seems that these snakes must be regarded as specimens 

 of E. elegans, showing a more or less uniform dark olive color with a 

 wide yellow dorsal stripe and little or no indication of laterals, cor- 

 related with a tendency to a reduced number of scale rows, and occur- 

 ring, as far as is known, in a restricted area. Such a form requires 

 recognition as a subspecies, for which the proper name obviously is 

 Eutcenia elegans atrata Kenn. Cope's name E. infernalis vidua being a 

 pure synonym. 



Anomalies such as these, occurring in some numbers and over a 

 period of at least some generations, belong to the mutations of De Vries, 

 but their proper assignment to any one of his special categories of the 

 constituent parts of species i? not so clear. It was pointed out on a 

 previous occasion that E. sirtalis, with nineteen rows of scales, is prob- 

 ably the parent species of the genus, in which case the occasional 

 appearance of that number in a species normally possessing twenty-one 

 rows might be, in De Vries' view, an outbreak of a tendency to specific 

 reversion to that number, and would fall under the definition of ata- 

 vistic or degressive varieties; but, on the other hand, it is difficult to 

 show, and would indeed be impossible when there is no knowledge 

 of the line of descent, that the case may be no more than individual 

 loss of two rows, a view to which color is lent by the further reduction 

 in three specimens to seventeen rows. This mode of change would 

 class them as retrogressive varieties. And again, the gain of a new 

 color-pattern, occurring nowhere in a possibly ancestral form, brings 

 them within the definition of elementary species. In fact, these speci- 

 mens seem to demonstrate the lack of value of these theoretical defini- 

 tions to the practical work of the systematist. 



The evidence for the evolutionary value of mutations being so scanty 

 among animals, it is not amiss to direct attention to the instability 

 of nearly the whole genus Eutcenia, and especially the species of the 

 Pacific coast. This condition suggests that if the theory of alternating 

 periods of stability and mutation be well founded, this group of species 

 may at the present time be passing through a period of extreme muta- 

 bility. 



October 17, 

 The President, Samuel G. Dixon M.D., in the Chair. 

 Forty-two persons present. 



The death of Sutherland M. Prevost, a member, September 30, 1905, 

 was announced. 



