148 STUDIES IN GEOLOGY, No. 3 



Cytherea planivieta Guppy, Quart. Jour. Geol. Soc. Lond., vol. 

 32, p. 531, 1876. 



Cytherea planivieta Grzybowski, Neues Jahrb., Beil. Bd. 12, p. 

 639, pi. 19, fig. 3, 1899. 



Pitaria (Lamelliconcha) planivieta Dall, Trans. Wag. Inst, vol. 

 3, pt. 6, p. 1268, 1903. 



Pitaria planivieta Maury, Bull. Amer. Pal., vol. 5, No. 29, p. 217, 

 pi. 37, fig. 3, 1917- 



Pitaria (Lamelliconcha) planivieta Woodring, Mollusca Bowden 

 Beds, Jamaica, Ms. 



With the slight exception, as noted by Grzybowski, that 

 the concentric rugae are a bit more crowded, there is no 

 essential difference between the forms from Peru and those 

 from the lower Miocene of the Antilles. The concentric 

 sculpture of the Peruvian form is slightly different, the 

 rugae giving the appearance of being less regularly placed, 

 but a distinction on the basis of that feature would be 

 valueless. The hinge of the Peruvian specimens is some- 

 what broader and heavier than that of planivieta from the 

 Bowden beds, but the elements are the same. One specimen 

 from Peru attains dimensions somewhat greater than those 

 usual in the Antillean planivieta. The forms in the Hopkins 

 collection were found in the Lower Zorritos formation. 

 Grzybowski's forms were taken from beds which he called 

 Heath, but which are known to be part of the Variegated 

 formation. The species thus has a known range in Peru 

 from the Lower Zorritos to the upper Variegated. 



Pitaria- aequicincta, from the uppermost Upper Zorritos, 

 undoubtedly represents a further development of the plani- 

 vieta strain. It is so close to planivieta that some delibera- 

 tion preceded its separation, but its sculpture is sufficiently 

 different to make advisable its consideration as another 

 species. In addition to the difference in sculpture the lack 

 of a well defined lunule in aequicincta marks another point 

 of departure, and makes the entity of the species more 

 eminent. In general contour the two are identical. Length 



