1916] 



Dickerson: Tejon Eocene of California 



481 



DESCRIPTIONS OP NEW SPECIES 

 Pelecypoda 



ACILA GABBIANA, n. sp. 

 Plate 36, figure 1 



Shell small, oval with straight anterior dorsal margin which 

 slopes steeply to a sharp angle, the junction of broadly rounded 

 ventral margin ; posterior dorsal margin gently convex ; posterior 

 end, narrowly rounded ; decoration consisting of delicate divaricate 

 sculpture crossed by incremental lines ; lunule fairly definite ; 

 escutcheon long and narrow. 



This species differs from Nucula truncata, with which it has fre- 

 quently been confused, in the following repeets: it is smaller, its 

 divaricate sculpture is more delicate, its escutcheon is more definite 

 and concentric sculpture is more regular. 



Named in honor of William Gabb, pioneer palaeontologist of the 

 Pacific Coast. 



Dimensions. — Height, 6 mm.; length, 9 mm. 



Occurrence. — The type was found at University of California 

 Locality 1817, lower Tejon beds, north of Coalinga. It has been 

 reported from many other Tejon localities, from the lowermost zone 

 of the Tejon to the uppermost. It may also occur in the Martinez 

 group as the form listed as Nucula cf. truncata Gabb may be this 

 species. 



ARCA CLARKI, n. sp. 

 Plate 37, figure 12 



Shell small, subquadrate, with height almost equal to length ; 

 beak inconspicuous, rounded, central ; anterior margin nearly 

 straight, extending from a bluntly pointed end to a broadly rounded 

 ventral margin ; posterior end broadly arcuate ; dorsal margin 

 straight; decoration consisting of acute ribs with interspaces about 

 twice their width. 



The more quadrate shape of this species distinguishes it from 

 A. hornii Gabb. 



Named for Dr. B. L. Clark. 



Dimensions. — Length, 4 mm. ; height, 3.5 mm. ; convexity, 1.5 mm. 

 Occurrence. — University of California Locality 733. 



