391 Costa Rica Miocene — Olsson 119 



to a small smooth nucleus; succeeding whorls are sculptured with 

 heavy persistent, straight ribs (13 or 14) on the last whorl; the 

 ribs are crossed by even, raised, spiral cords; the spire- whorls 

 have 4 spiral cords and a small one close to the upper suture; an- 

 terior canal short and strongly twisted; aperture subelliptical, 

 the outer lip with about 10, strong and regular internal lirse. 



Height 27, diameter 12, last whorl 17, spire 14 mm. 



This is the common Phos of the Banana River. Although 

 closely related to Moorei, from Jamaica, the Costa Rican fos- 

 sils are smaller and more slender, as compared with Guppy's 

 figure in the Ouarterlj^ Journal, vol. 22, pi. 16, fig. 11. 



Dr. Maury's Phos Moorei, from the Miocene of Santo Do- 

 mingo probably represents a distinct species, differing by its 

 more slender spire, and in sculpture. The spiral intervals of 

 costaricensis are smooth, w^hile in the Santo Domingan shells, 

 they carry fine spiral threads, which are best seen on the spire- 

 whorls, sometimes becoming obsolete on the later. 



Gatun Stage: Banana River, 



Old Man Sa7n Creek, i mile from shore or 

 beach. 



Phos elegans Gupp, var. limonensis, n. var. Plate 9, figures 12, 13 



Shell usually smaller, more slender and delicate than the pre- 

 ceding species; the spire is long, composed of about 9 whorls: 

 the nucleus consists of 4 whorls, the first 2 are small, 

 smooth and convex, the last 2, smooth, but sharply keeled about 

 the periphery on the last 1-4 of the last nuclear whorl, faint 

 curved lines appear above the peripheral keel, they gradually in- 

 crease in strength and on the ist post-nuclear whorl become the 

 longitudinal ribs; the sculpture consists of fine, longitudinal ribs 

 (23 or 24 on the last whorl); occasionally a rib may become 

 greatly enlarged, forming varix-like thickenings corresponding 

 to resting stages; the ribs are overrun by primary, secondary and 

 tertiary spiral threads; the later spire whorls have about 6 spirals. 



