164 STUDIES IN GEOLOGY, No. 3 



Surface gently and evenly convex. Shell almost entirely 

 smooth, but with microscopic sculpture of very fine con- 

 centric growth-lines. There is an impressed area on the 

 cast before the beak; no escutcheon is evident. Inner shell 

 not known. Length, 32.5; height, 12; (semi) diameter 

 approx. 2 mm. 



Fragmental impressions in matrix from the Lower Zor- 

 ritos give evidence of the abundance of this species, but its 

 extreme fragility almost precludes its extraction from the 

 hard rock in which it occurs. It is unfortunate that only 

 one specimen could be laid bare in sufficient entirety to 

 justify attention ; however, enough may be observed of 

 that one to note its important external characters, and such 

 observation shows it to be almost certainly new. 



It is very much like Solen dombeyi Lamarck, 189 described 

 by Philippi from Coquimbo, Chile, but is much smaller and 

 apparently more delicate. Fragments noted in matrix indi- 

 cate that S. plamifolliculus probably grew to no greater size 

 than that of the specimen described. 



Solen tenuis Philippi, 190 from Chile, is represented by 

 its author as a cast with two pieces of the shell adhering, 

 and although it is a form of apparently the same size and 

 delicacy of S. planifolliculus, the shape indicated by Philip- 

 pi's cast differs in being arcuate ventrally whereas plani- 

 folliculus is ventrally straight or very slightly sinuate. 



Lower Zorritos. Head of Quebrada Zapotal. 



Los. Fos. Terc. y Cuart. de Chile, p. 163, pi. 34, fig. 5, 1887. 

 Idem., fig. 7. 



