Paleontology Zorritos Formation 131 



Lower Zorritos. Ridge at head of Quebrada Heath. 



Crassatcllites (Scambulaj bcrryi n. sp. 



Pl.\te VII — Figs. 9, 10. 



Shell of medium size, anteriorly inflated, posteriorly atten- 

 uate. Anterior margin rounded ; ventral margin rounded 

 anteriorly, ascending posteriorly in a reflex curve to the 

 apex of the first of two marginal angles. The posterior 

 dorsal margin is about straight, descending to meet the 

 apex of the second posterior marginal angle. Umbones 

 high, erect, inflated, prosogyrate, proximate, the tops flat- 

 tened, with the flat surface sloping backward. Anterior 

 surface convex. A prominent keel, sharp on and near the 

 beaks and flattened ventrally, runs from the umbo to the 

 lower marginal angle; before the keel there is a sulcus, 

 narrow and sharp umbonally and shallower ventrally. Be- 

 hind the posterior half of the keel is a flat to concave surface 

 which is often bounded posteriorly by a second vestigial 

 keel. Sculpture of strong concentric undulations, their 

 dorsal slopes steeper, sharp on the beaks and decreasing in 

 prominence ventrally but evident over all of the shell, sharper 

 anteriorly on the median surface. There is additional sculp- 

 ture of fine growth-lines. The concentric sculpture parallels 

 the margins. Lunule deeply impressed, distinct, oval : es- 

 cutcheon of similar lines but more lanceolate. Hinge nor- 

 mal. Muscle scars deeply impressed; internal valve-margins 

 smooth ; parallel line sharp. Length, 40.5 ; height. 28 ; diam- 

 eter, 20.5 mm. 



This form differs from Crassatcllites nclsoni. chieflv in 

 the possession of strong concentric undulations over most or 

 all of its surface instead of on the beaks alone. This sculp- 

 ture tends to become obsolete on the ventral-posterior part 

 of the shell, but it is clearly marked elsewhere on all speci- 

 mens, and some show it almost equally strong over the entire 

 shell. The beaks are not as prominently flattened as in ncl- 



