478 University of California Publications in Geology [Vol. 8 



This species sometimes has a length of six to eight inches and a 

 height of from one inch to one and one-half inches. It is the most 

 common Solen in the Miocene and Pliocene of California. It has been 

 listed by various writers as Solen sicareus Gould and Solen rosaceus 

 Cpr. It differs from S. sicareus in that both the posterior dorsal edge 

 and the ventral edge are straight. S. sicareus shows a slight concavity 

 along the posterior dorsal edge, while the ventral edge is slightly con- 

 vex. Also S. sicareus has very little, if any, flexture on the anterior 

 end. S. perrini resembles S. rosaceus more closely than S. sicareus. 

 It differs in that it is a heavier shell; and it is higher in proportion 

 to its length. 



Named in honor of Professor James Perrin Smith of Leland 

 Stanford Junior University. 



Locality. — Upper and Lower San Pablo Group. 



MYA DICKEKSONI, n. sp. 

 Plate 63, figures 3 and 4 



Shell somewhat variable in outline, elongate-subovate ; beaks incon- 

 spicuous, usually anterior to the middle of the shell. Valves more 

 ventricose anteriorly than posteriorly ; posterior end truncated ; an- 

 terior end evenly rounded; posterior dorsal edge long, nearly straight, 

 on some specimens slightly concave ; anterior dorsal edge gently ar- 

 cuate; ventral edge long, very nearly straight, almost at right angles 

 to the truncated edge of the posterior end. Surface of valves rather 

 strongly excavated anterior to the beaks; covered by rather coarse 

 undulations on and between which are finer incremental lines; chon- 

 drophore large with a prominent radiating ridge near the posterior 

 edge projecting beyond the edge even more prominently than is the 

 case with the same ridge on Mya arenaria Linne, a Recent species. 



M. clickersoni differs from M. japonica Gould and M. arenaria 

 Linne, both Recent species, in that it is truncated posteriorly and the 

 ventral edge tends to be less arcuate. 



M. dicker sonii resembles M. truncata, a Recent species, in that it 

 is truncated posteriorly nearly at right angles to the ventral edge. It 

 differs in being more elongate; the anterior end is not so broadly 

 rounded, and the posterior end is narrower ; the posterior dorsal slope 

 is longer ; the posterior ridge on the chondophore extends out beyond 

 the edge, on M. truncata it does not. 



