14 H. Doc. 129. 



Locality. Occurs with the preceding shell. Recent formation. 



One broken valve of this species occurred in the same specimen of 

 rock in which they had bored. Some specimens of the Saxicava are 

 entire, and fill the cavities they have formed, when living. 



SCHIZOTHCERUS, Conrad. 



28. s. NUTTALLI, Con., pi. iii, fig. 33 and 33a. Ovate, ventricose, 

 gaping widely posteriorly ; moderately thick in substance ; anterior 

 side short, abruptly rounded at the extremity ; posterior side elongated, 

 extremely truncated ; dorsal line slightly concave ; umbo not promi- 

 nent ; basal margin profoundly rounded ; hinge-plate broad, cartilage 

 pit large, obliquely ovate, profound ; cardinal teeth in the left valve 

 two, one in the right valve ; anterior cardinal plate broad, with an 

 angular depression throughout its entire length, posterior one narrow, 

 with a deep angular channel in which is a bifid plate in the right 

 valve; cavity of shell and umbo profound. 



Locality. San Pedro in calcareous marl. Recent formation. W. 

 P. Blake. 



I have referred this shell to the same genus in which I placed 

 Lutraria Nuttalli of the California coast. The hinge is very similar to 

 that of Lutraria, but the long deep channels of the hinge are similar 

 to those of L. Nuttalli, the animal of which differs from that of Lutraria. 

 I do not know of any recent species of the latter genus in California. 



LUTRARIA? Lam. 



29. L. TRASKEI, Con., pi. iii, fig. 30. Suboval, ventricose, inequi- 

 lateral, hinge and basal margin nearly parallel ; posterior margin 

 subtruncated and slightly oblique, or approaching a direct outline ; 

 posterior extremity rounded. 



Locality. Carmello. Miocene? (Received from John B. Trask, 

 by whom it was collected. W. P. S.) 



MACTRA, Lin. 



30. M. DIEGOANA, Con., pi. iv, fig. 35. Triangular ventricose, ine- 

 quilateral, anterior side oblique, rectilinear ; umbonal slope carinated 

 and nearly terminal ; basal margin profoundly and regularly rounded. 



Locality. San Diego. Miocene? 



This species is nearly allied to M. albaria of the Oregon Miocene, 

 which probably belongs to the same rock as the present species. The 

 concentric ridges represented in the figure are caused by weathering, 

 as the disk was originally smooth. 



MODIOLA, Lam. 



31. M. CONTRACTA, Con., pi. iv, fig 35. Elongated, narrowed, an- 

 teriorly, contracted submedially; basal margin widely contracted; 

 disk with numerous minute radiating lines. 



Locality. Monterey Co., 18 miles S. of Tres Pimos. Recent forma- 

 tion. 



A portion of the shell remains, showing traces of fine radiating 

 lines. Miocene? 



