1896. | NEW YORK ACADEMY OF SCIENCES. 157 
graphic film and suspending a magnet in front of them. No 
satisfactory explanation or theory of the results has been given. 
(5) In conclusion Mr. Levison pointed out certain causes which 
in his opinion might account for the deterioration of photo- 
graphic plates, suggesting among other things X-rays from un- 
expected sources, terrestrial magnetism, plant organisms and 
gases sucb as sulphuretted hydrogen penetrating the boxes and 
injuring the plates. He suggested the improvement of enclosing 
the plates in soldered metal boxes. These notes were discussed 
by Prof Mayer and Prof. Hallock. 
By permission of the Section Mr. C. C. Trowbridge read by 
title a paper entitled “ The Use of the Hair Hygrometer.” 
On motion the section adjourned. ° 
J. F. Kemp, Wm. HALtock, 
Secretary. Secretary of Section. 
STATED MEETING. 
May 11th, 1896. 
The Academy met with Vice-President Osporn in the chair. 
The reading of the minutes of the last meeting was postponed. 
The following papers were read : 
ON THE VERTEBRAL COLUMN, FINS AND VENTRAL 
ARMORING OF DINICHTHYS. 
By Basurorp DEAN, 
Department of Zodlogy, Columbia University. 
Hitherto our definite knowledge of this most interesting of 
American Arthrodiran fishes has been limited to the structures 
of the anterior body parts—the jaws and the plates of the head, 
“shoulder” and abdomen. It was upon these characters, as 
described in several species, that the inference had been made 
that Dinichthys was closely akin to the European Coccosteus. 
But any satisfactory comparison of the relations of these 
kindred Arthrodirans could, it is evident, only be made when 
