Bulletin 39 270 



solid and with a lower and less diiTerentiated spire; whorls 4 or 

 more with sutures scarcely distinguishable under their glaze or 

 coat of callus; aperture linear-elongate, widest in front and 

 slightl}^ contracted in the middle; outer lip thickened, smooth 

 within; pillar with 4, oblique plaits of nearly equal strength. 



Length II, diameter 4.5, spire 1.5 mm, 

 10 4-25 I mm. 



11.25 5- I mm. 



Closely related to the Margiriella avena VaL, this species 

 differs in being more solid, less slender and with a lower spire. 

 In avena the spire is clearly differentiated, with well marked su- 

 tures to its spire-whorls. In the present shell, the spire is much 

 lower, and the sutures are more thickly covered with glaze. The 

 thick outer lip is carried across the end of the lip and firmly 

 joined to the spire without any preciptible line of demarcation. 

 In avena, the outer lip and spire are clearly differentiated from 

 each other. 



Abundant in the Gatun beds of the Banana River. 



Gatun Stage: Hill la, Banana River. 



MargineSia leander Brown and Pilsbry Plate 6, figure 22 



Marginella leander' Brown and Pilsbry, 1911, Proc. Acad. Nat. Sci. 

 Phila., vol. 63, p. 347, pi. 24, fig. 13. 



Not known from Costa Rica, and the figure here given is 

 from a specimen in our collection from Gatun. It is a broader 

 and more cylindrical species than collina, and with a much low- 

 er and scarcely elevated spire. Our specimen measures 9 by 4 

 mm. 



Gatuyi Stage: Gatun, C. R. 



Marginella musacina, n. sp. Plate 10, figure 25 



Shell small and slender, with a high spire of about 1-4 of 

 the total length of the shell; whorls about 5, with sutures light- 

 ly concealed under a thin coat of glaze; last whorl narrowly cylin- 



