PLATE XVI 



TOPOGRAPHY OF BIVALVE SHELLS 



1. Integropalliata : Cardium pseudolima, Lamk. 



2. Sinupalliata : Mercenaria Mortoni, Conrad. 



3. Four specimens showing stages in the disappearance of 

 anterior adductor muscle : 



the 





A, Glycimeris latitans. 







B, Cardita crassicostata 



Lamk. 





C, Mytilus Calif omianus, Conrad. 





D, Meleagrina barbata, 



Reeve. 



a. a. 



Scar of anterior adductor 



m. 



, Scars of pallial muscles. 





muscle. 



p.a. 



, Scar of posterior adductor 



a.m. 



Anterior margin. 





muscle, 



a.p.a. 



Area of pallial attach- 



p. 1. 



Pallial line. 





ment. 



p.l.t. 



Posterior lateral teeth. 



c.t. 



Cardinal teeth. 



p.m. 



Posterior margin. 



d.m., 



Dorsal margin. 



p.r. 



Scar of pedal retractor 



h.l., 



Hinge line. 





muscle. 



h.p., 



Hinge plate. 



p.s. 



Pallial sinus. 



1., 



Ligament. 



11 



Umbo. 



1. a., 



Ligamental area. 



7i. a., 



Umbona! area. 



he, 



Lunule. 



v.m., 



Ventral margin. 



{Reproduced, by permission of the Trustees, from Photographs of Specimens on 

 Exhibition in the Natural History Museum.'] 



