1912.] NATURAL SCIENCES OF PHILADELPHIA. 507 



whorls with sculpture of rounded axial ribs nearly as wide as their 

 intervals, crossed by spiral cords. On the last whorl there are 

 13 or 14 ribs, the last one larger, forming the lip-varix. The ribs 

 are continuous from whorl to whorl as in some related forms. Spiral 

 sculpture of low cords which are more prominent on the ribs, weak 

 in the intervals, and to the number of eight on the last whorl above 

 the basal sulcus. On the penultimate whorl there are three of 

 these cords, lower than those on the last whorl, or sometimes 4 

 when the upper one is split. The aperture is small, apparently 

 not unlike that of N. ambigua, but filled with coarse material in all 

 the specimens. 



Length 5.3, diam. 3.3 mm. 



From a lignitic clay below the Pecten bed at Tower N, Culebra 

 Cut. The specimens were taken from 65 to 80 feet below the 

 Pecten bed. It is rather abundant. 



In Nassa ambigua there are more spiral cords than in this species, 

 and they are stronger in the intercostal intervals; the whorls of the 

 spire are more convex. In N. prceambigua the spire is straight- 

 sided as in N. vibex Say. N. bidentata Emmons has fewer spirals 

 and wider, fewer axial ribs. The recent Alectrion (Hima) catallus 

 Dall, from deep water in the Gulf of Panama, is a more elaborately 

 sculptured shell of the same group. N. prceambigua is probably 

 an ancestor of the Pliocene and recent members of the Hima group 

 on both sides of the isthmus. 



Pyrula micronematica n. sp. PI. XXII, fig. 8. 



The shell has the usual shape. Sculpture of small, slender spiral 

 cords which are noticeably knotted where the rather wide-spaced 

 axial threads intersect them. Minute secondary spiral threads 

 divide the wide spaces of the primary cords. Faint traces of most 

 minute spiral threads of a third order may be perceived. The 

 spacing and number of spirals is the same as in the recent P. decus- 

 sata Wood. 



Length of the imperfect specimen figured 28.8 mm. 



Found in the Pecten bed in the Culebra Cut near Tower N, Las 

 Cascades. 



This species agrees with Pyrula decussata Wood of the recent 

 Panamic fauna in having only half as many major spirals as the 

 Antillean P. papyracea Say and P. pUsbryi B. Smith. The essential 

 differences between the two collateral phyla (represented in the 

 recent fauna by P. papyracea and P. decussata), were therefore 



