u 



predorsal fin spine, a double spine, not co-ossified. Three new 

 types were described, two of them naked of scales, and the 

 third covered only with rudimentary scales. 



Prof. Cope communicated a short note entitled, " On the 

 Zoology of a Temporary Pool on the Plain of Colorado." 



Mr. Blasius, of Philadelphia, present by invitation, exhi- 

 bited maps and pictures of the tornado of August 22d, 1851, 

 in Cambridge and Medford, Mass., and described his survey 

 and study of the same, the impossibility of applying Red- 

 field's theory except to its central, and Espy's to its ultimate 

 track ; for the initial division another explanation was 

 requisite. This led him to the study of the general pheno- 

 mena attendant upon the meeting of the equatorial and 

 boreal currents, the determination of the shape of land and 

 ocean gales, the use of clouds and their shapes and positions 

 for indicating the nature and position of approaching storms, 

 and the construction of practical sailing directions for vessels 

 in danger. 



Mr. Briggs said that he happened to see the tornado 

 referred to, and gave an account of its aspect, efiects, and 

 the part of the track which he afterwards examined, by 

 which he was led to the conviction that it was locally deter- 

 mined, like other similar storms, by the low ground of 

 Charles River, heated to an unusually high temperature in 

 a calm day. 



Mr. Lesley replied that the constant eastward movement 

 of these tornados, and their sometimes immense length, 

 together with their well known repeated occurrence along 

 the same lines of country, proved them items of an extensive 

 system of phj^sical conditions in the atmosphere on the shift- 

 ing line of meeting of the equatorial and polar currents, as 

 Mr. Blasius had so well described, and that he hoped the 

 acknowledged defects of the present tornado sailing direc- 

 tions would be corrected by those indicated by the theory 

 of Mr. Blasius. 



Pending nominations 'Nos. 745 to 749, and new nomina- 

 tions 750, 751, were read. 



And the meeting was adjourned. 



