No. 436.] APPENDAGES OE TREMATASPIS. 



233 



apparently made by the attachment of powerful muscles. The 

 floor of each depression is irregularly ridged, and has a dull, 

 almost shining, surface. At its posterior end is a still deeper 

 rounded depression, m. m., 2 that probably served for the attach- 

 ment of a special group of muscle fibres. The rounded depres- 

 sion is considerably deeper and more clearly defined on the right 

 side of the plate. 



