212 Kansas Academy of Science. 



42. Mactra exoleta Gray. Plate IV, figs. 42a., 426. 



Mactra exoleta Gray, equals Lutraria ventricosa Gld. {fide Carpenter, Proc. 

 Zool. Soc, 1856, p. 200). Arnold, Mem. Cal. Acad. Sci., vol. Ill, p. 175, 

 pi. XIX, fig. 4, 1903. 



Arnold's description : " Shell of medium size, decidedly trigonal, 

 ventricose, thin, fragile ; umbones slightly anterior to center, ele- 

 vated, not touching, turned only slightly forward ; anterior dorsal 

 margin straight ; anterior extremity evenly rounded near base ; 

 ventral margin evenly arcuate ; posterior dorsal margin arcuate, 

 making an acute angle with the ventral margin ; a sharp, promi- 

 nent, angular ridge runs from umbo to the posterior extremity ; 

 surface sculptured with fine, incremental lines, which are most 

 prominent posterior to ridge ; cartilage-pit deep ; hinge teeth lamel- 

 lar, long ; ligamental groove very deep, narrow." 



This species is well represented in the Quillayute formation at 

 the mouth of Maxfield creek, opposite Quillayute, Wash. 



Living : Coast of Mexico. 



Pleistocene: San Diego, San Pedro, Cal. (Arnold). 



Pliocene : Quillayute, Wash. (Reagan). 



43. Mactra hemphilli Dall. Plate IV, fig. 43. 



Mactra hemphilli Dall, Nautilus, vol. VII, 1894, p. 137, pi. V; Arnold, Mem. 

 Cal. Acad. Sci., vol. Ill, p. 175, pi. XIX, fig. 3, 1903. 



The classification of this shell is based upon its having its an- 

 terior portion hollowed in front of umbo, making the dorsal margin 

 slightly concave, as is a leading characteristic of the species; in- 

 terior of valve not seen. Shells collected are all small and immature. 



vShell subtrigonal, subequilateral, convex, thin; umbones sub- 

 central, slightly elevated, turned slightly forward; anterior end 

 evenly rounded; posterior dorsal margin evenly arcuate; posterior 

 end most produced near base: surface sculptured with fine incre- 

 mental lines. 



This is an abundant species in the Quillayute formation at the 

 old mouth of Maxfield creek. 



Pleistocene: Sari Pedro, Cal. (Arnold). 



Pliocene: Quillayute, Wash. (Reagan). 



43J. Mactra catiliformis L 



Only a fragment of a shell was obtained, which is doubtfully 

 classed as above. The posterior and anterior dorsal margins have 

 the same declining angle from the beak as M. catiliformis : but 

 the characteristic fold posteriorly is lacking. 



Shell found arriong the other Madras from the Quillayute for- 

 mation. 



