146 Scientific Intelligence. 



taken from a species described four years after the genus is 

 proposed, especially as the original type belongs to a different 

 genus from that of the species taken as the type at a later date. 

 Mr. Billings, in his original comparison of A. Ailanticus and 

 A. Minganensis, says : " It may be that these two species 

 should be placed in different genera," and repeats the remark 

 in the reprint of 1865 ; but, in the latter, the name A. Mingan- 

 ensis is replaced by A. profundus. 



In my remarks upon the genus Ethmoplryllum (Bull. 30, U. 

 S. Geol. Survey, p. Y5), I called attention to the publication, in 

 vol. ii of the Geology of Vermont, of the genus Archeocyathus. 

 At that time I was not aware of the fact of the prior publica- 

 tion of the pamphlet by the Geological Survey of Canada, nor 

 that the Geology of Vermont was issued in 1862 and not in 

 1861 — the date on the title-page. I am indebted to Professor 

 Jules Marcou for calling my attention to the existence of the 

 pamphlet of 1861 and to the date of the publication of the 

 Geology of Vermont, as 1862. It is noted, in the Geology of 

 Vermont, that the descriptions were taken from a pamphlet 

 sent by Mr. Billings, but not being able to obtain any trace of 

 the pamphlet, as a publication at the time, I referred the origi- 

 nal description to the Geology of Vermont, vol. ii. 



I have written the above explanation, owing to having 

 received a letter from a distinguished paleontologist, who ques- 

 tioned the propriety of using the genus Ethmophyllum for the 

 generic type, so well illustrated by Ethmophyllum Whitneyi and 

 E. profundam. I did not feel warranted when describing the 

 genus in Bull. 30, U. S. Geol. Survey, in proposing a new 

 genus for Archeocyathus Ailanticus, or in placing Ethmophyllum 

 as a synonym of Archeocyathus ; and since reading the origi- 

 nal pamphlet of Mr. Billings, I am disposed to adhere to the 

 views which I then held on this subject. 



SCIENTIFIC INTELLIGENCE. 



I. Physics and Chemistry. 



1. On the Cause of Iridescence in Clouds ; by G. Johnstone 

 Stonet. — When the sky is occupied by light cirro-cumulus cloud, 

 an optical phenomenon of the most delicate beauty sometimes 

 presents itself, in which the borders of the clouds and their lighter 

 portions are suffused with soft shades of color like those of 

 mother-of-pearl, among which lovely pinks and greens are the 

 most conspicuous. Usually these colors are distributed in irreg- 

 ular patches, just as in mother-of-pearl ; but occasionally they are 

 seen to form round the denser patches of cloud a regular colored 



