352 PROCEEDINGS OF THE ACADEMY OF [April 



close to the ancestral stock of A. avara. Two Pliocene forms have 

 features possibly derived from this Oligocene form, combined with 

 various diverse characters : A. avara caloosaensis Dall, in the Floridian 

 Stage, is more robust than A. fugax, the number of sculptured whorls 

 is greater and the suture specially modified. A. camax Dall, from a 

 slightly later stage, and even more like A. fugax, differs by having 

 but "two smooth and eight reticulated whorls," and the spiral sculp- 

 ture is far more strongly developed. 



In both of the Pliocene species there has been acceleration of the 

 sculpture since the Oligocene form, A. fugax having about 5^ smooth 

 and 3 to Z\ sculptured whorls. In various other Pliocene and recent 

 forms of the same stock, however, there has been retardation of 

 longitudinal sculpture, which first appears on the last whorl. 



Anachis styliola Dall is a form superficially similar to A. fugax, but 

 unlike it in the important feature of having a large, bulbous embryonic 

 shell. 



♦Strombina mira Dall. 



S. mira Dall, Proc. U. S. Nat. Mus., XIX, p. 312. PL 29, fig. 7. 



Oligocene marl, near Gatun (Rowell, Hill). 

 Strombina lessepsiana n. sp. PI. XXV, figs. 11, 12. 



A species closely related to S. cyphonotus and S. prisma, but more 

 slender than either; fusiform. Spire when perfect of fully 11 whorls, 

 the suture distinctly, though not conspicuously channelled, ascending 

 at the end less than in the other species. Last whorl subtriangular 

 in transverse section, having a strongly oblique node on the left side, 

 a low dorsal hump near the suture, and marked with several sharp 

 wrinkles, and behind the outer lip a strong varix preceded and followed 

 by a concavity. At the base there are strong spiral grooves, 11 to 

 15 in number. Under the lens very weak traces of spiral sculpture 

 may be seen on the almost smooth later whorls. Aperture as in S. 

 prisma, but with the canal slightly longer. 



Length 27.0, diam. 10.0 mm. (apex entire). 

 " 22.2, " 9.2 " (apex broken). 

 " 26.2, " 10.0 " 



Not uncommon at Gatun. It is even more slender than S. prisma, 5 



5 We introduce here descriptions of S. prisma and S. cyphonotus from Johnson 

 and Pilsbry's report on Gabb's Santo Domingo fossils (not yet published), in 

 order to demonstrate the relationships of S. lessepsiana. 



" Strombina prisma P. and J., n. sp. PI. XXV, figs. 9, 10. 



"The shell resembles S. cyphonotus, but differs by being more fusiform, the 

 obliquely longitudinal hump or node on the left side is stronger, dorsal hump 



