154 Studies in Geology, No. 3 



It is interesting to note that all of the Chiones s.s. known 

 from the Zorritos formation have the double ribs which 

 are a characteristic feature of Chione zualli Guppy, a com- 

 mon point which serves to emphasize their relationship not 

 only to one another, but to the Chiones of the Trinidad 

 beds of slightly earlier age. A number of unstudied forms 

 from probably younger horizons in Ecuador show this 

 feature clearly. 



Lower Zorritos. Quebrada Zapotal. 



Section Lirophora Conrad 

 Chione (Lirophora) hendersonii Dall 



Venus paphia Guppj', Quart. Jour. Geol. Soc. Lond., vol. 22, p. 

 292, 1866; (not of Linnaeus, 1758). 



Chione paphia Gabb, Trans. Amer. Phil. Soc. n. s., vol. 15, p. 249, 

 1873. 



Venus paphia Guppy, Geol. Mag., dec. 2, vol. i, p. 442, (check 

 list) ex parte, 1874; (not of Linnaeus). 



Venus paphia Guppy, Quart. Jour. Geol. Soc. Lond., vol. 32, p. 

 530, 1876; (not of Linnaeus). 



Chione (Lirophora) hendersonii Dall, Trans. Wag. 'Inst., vol. 3, 

 pt. 6, pp. 1295-1296, pi. 55, fig. 22, 1903. 



Chione (Lirophora) hendersonii Maury, Bull. Amer. Pal., vol. 5, 

 No. 29, p. 219, pi. 37, fig. 8, 1917. 



Chione (Lirophora) hendersonii Woodring, ]\Is. 



This species is common in the Bowden beds of Jamaica, 

 and occurs also in the lower Miocene of the Dominican 

 Republic. In its Antillean occurrences it is somewhat 

 variable in form, ranging from more convex forms with 

 higher beaks, more incurved anterior margin, steeper 

 posterior slope, and wider cardinal areas to those with these 

 characters at the opposite extreme. To quote Woodring 

 (Ms) "the species is characterized by its rather numerous 

 ribs and the relatively wide posterior area over which the 

 ribs are lower and sharper. The form mentioned in the 



