82 University of Washington Publications in Geology [Vol. 1 



Dimensions Altitude 7 mm.; longitude 13 mm.; thickness 5 mm. 



Occurrence At locality 364 (University of Washington Paleontological Col- 

 lection) situated at the old dam on Porter Creek about two and one-half miles 

 above its junction with Chehalis River in Section 14, Township 17 North, 

 Range 5 West. 



Horizon Lowermost Oligocene; Barbatia merriami Zone. 



GENUS MYTILUS LINNAEUS 



MYTILUS BUWALDANA n. sp. 

 Plate VI, Figure 6 



Description Shell of moderate size, elongate, ventricose, moderately thick; 

 liinge line nearly straight; the posterior dorsal margin slightly concave. At a 

 distance of three-fourths the length of the shell from the anterior end the surface 

 slopes rapidly to form a broadly rounded posterior margin where it merges at a 

 Tery sharp angle into a slightly concave base. The maximum width of the shell 

 is situated about one-third the length of the shell from the posterior end. A very 

 pronounced umbonal ridge extends from the beaks through the middle portion of 

 the shell and terminates near the junction of the ventral and posterior margins. 

 This ridge is most strongly pronounced near the middle portion of the shell. Surface 

 of shell is sculptured by very prominent concentric lines of growth, giving the surface 

 of the shell a roughened appearance. 



Dimensions Altitude 21 mm.; longitude 38 mm.; thickness 18 mm. 



Occurrence At locality 161 (University of Washington Paleontological Col- 

 lection) about one mile west of Oakville on the Northern Pacific Railway. 



Horizon Lowermost Oligocene; Barbatia merriami Zone. 



GENUS MODIOLUS LAMARCK 

 MODIOLUS RESTORATIONENSIS n. Sp. 



Plate VI, Figure 5 



Description Shell of moderate size and somewhat elongate; hinge line nearly 

 straight and about two-thirds the length of the shell. The posterior dorsal margin, 

 which is nearly straight, extends to the posterior end of the shell, where it merges 

 abruptly into a very wide and broadly arcuate posterior margin. The maximum 

 height of the shell is at the posterior end. The ventral margin is very slightly 

 concave; anterior margin is narrow and slightly arcuate; beaks low, anteriorly 

 pointed and very near to the anterior end. A well-defined umbonal ridge extends 



