Paleontology Zorritos Formation i6i 



parison of material shows the specific characters of the two 

 groups to be identical, and the small variation in the hinge 

 of the ZorritO'; specimens may be waived as of no systematic 

 importance. The occurrence of this beautiful and interesting 

 little shell in Peru extends its known range to cover the 

 area between Florida and Zorritos, and it may not im- 

 profitably be sought in the large collections from Gatun 

 now awaiting study at the United Sates National Museum, 

 as well as in beds of similar age in Ecuador and Colombia. 

 It differs from T. singeivaldi, in being smaller, longer in 

 proportion to height, and in having the median concentric 

 sculpture and ventral margin straight instead of arcuate. 



Tcllina ( Anguhisf) singez^.'oldi n. sp. 



Plate X — Fig. 5. 



Shell medium-sized, subequilateral. verv fragile, com- 

 pressed. Anterior margin rounded, somewhat produced ; 

 ventral margin slightly elliptical; posterior margin rounded, 

 shorter than the anterior. Umbones pointed, not prominent. 

 Surface generally flattened; a posterior keel is bounded on 

 either side by shallow sulci. Sculpture of fine growth-lines, 

 concentric, subangular at the posterior keel, evenly curved 

 elsewhere. Escutcheon small. Hinge not known. Pallial 

 sinus deep, extending nearly to anterior muscle scar. Pos- 

 terior muscle scar long and narrow. Length. 34 ; height. 23 ; 

 (semi) diameter, 2.5 mm. 



This species may be distinguished from T. zapotalcnsis, 

 of the local fauna, by its smaller size, greater fragility, 

 sharper posterior keel, and proportionally more pronounced 

 sculpture. In shape it is more nearly like T. maaica 

 Maury,^*® from the lower Miocene of Santo Domingo, than 

 is zapotalensis, but is not nearly as much inflated, the sculp- 

 ture is more angulate at the posterior keel, and the posterior 



Bull. Amer. Pal., vol. 5, Xo. 29. p. 222,, pi. 38, fig. 5, 1917. 



