172 REPORT ON THE STATE CABINET. 



EXPLANATION OF PLATE 1. 



Fig. 1. View of a specimen of Jltrypa reticularis from the Lower Helderberg group of Albany 

 county, N. Y., showing the form and position of the loop and spires. The view is 

 obliquely from above and behind. Enlarged. 



Fig. 2. Interior of a ventral valve ; from the same position and locality as the last, enlarged to 

 show the depressed area and sohd beak. 



Fig. 3. Interior of a ventral valve of A. reticularis from the Hamilton shales, showing the form 

 of the beak as existing in very perfect specimens ; for comparison with fig. 2. The 

 specimen is in Prof. Hall's collection, and the figure borrowed from the Pal. of N. Y., 

 Vol. IV. 



Fig. 4. An enlarged outline figure of the first volutions of the spires with the loop and crura 

 attached to the hinge-plate. The specimen from which the figure was drawn is from 

 the Falls of Ohio, and belongs to the collection of Prof. Hall, from whom it was 

 obtained for manipulation. 



Figs. 5 and 6. Dorsal and ventral views of a specimen from the shales of the Hamilton group of 

 New York, showing the form of spires and loop. 



Figs. 7 and 8. Dorsal and ventral views of a specimen oi Atrypa spinnsa, Hall, from the Hamil- 

 ton shales of New York, showing the form of spires and loop. Figs. 5-8 are natural 

 size. 



