170 
PALEONTOLOGY OF NEW YORK. 
the pedicle-muscles and the modification produced by the presence of the 
pedicle-passage, abstracted. 
In Crania and Craniella, where the sedentary habit appears to be no 
more than a specific character, there is little variability in the nature of the 
muscular scars; in the genus Pholidops, however, the shells of which are 
invariably free, there is a concentration of the muscular scars at the middle of 
the valves, the strength of the impressions indicating that considerable power 
was required to keep the valves closed, with the muscles placed at this dis¬ 
advantageous position. 
