24 
Explanation of Plate IV. 
Conchidium decussatus Whiteaves. 
Figure 1. Dorsal view of an exfoliated brachial valve showing an abnormal 
lateral sinus and constriction in the margin of the shell 
and varices of growth. 
“ 2-4. Ventral lateral and dorsal views of a natural cast of an ex- 
tremely gibbous form showing the angular median fold in each 
valve and the abnormal length and eccentric course of the septae 
in the brachial valve. 
