198 PROCEEDINGS OF THE ACADEMY OF 



as occurring in South America. There is another species, (P.) Strombus 

 semicostatus D' Orb., that occurs in the same deposit. 



Pleurotoma D'Orbignyana, pi. 3, fig. 7. Shell scalariform, spire ele- 

 vated, whorls five, body whorl angular above ; shell marked by a series of 

 small nodes on the shoulder of the whorls and by fine lines of growth. 



P. arata, pi. 3, fig. 9. Shell scalariform, spire elevated, whorls three or 

 four, subangular above and marked by a shallow, revolving groove imme- 

 diately below the angle ; surface marked by numerous revolving striae, crossed 

 by faint lines. 



Patella Auca, pi. 3, fig. 11. Shell small, thin, circular; apex small, 

 acuminate and very excentrio ; surface marked by irregular concentric undu- 

 lations. 



Cultellus Australis, pi. 3, fig. 8. Shell elongate, narrow, beaks very 

 small, incurved, near the anterior end ; posterior end gaping, and a little nar- 

 rowed ; anterior end rounded ; surface marked by concentric striae. 



Mactra Chiliensis, pi. 3, fig. 5. Shell thin, equilateral, slightly convex; 

 beaks small, incurved ; umbones large, prominent ; hinge teeth small ; ante- 

 rior end slightly subangular, posterior rounded ; surface marked by distinct 

 concentric lines. 



M. Araucana, D'Orb. sp. var. pi. 3, fig. 12. This specimen differs a lit- 

 tle from the one figured by D'Orbigny, in the Voyage de l'Astrolabe et Zelee, 

 in being less angular anteriorly, and in having the umbonal ridge less strongly 

 developed. 



Thracia corbulopsis, pi. 3, fig. 1. Shell nearly equilateral, beaks 

 small, slightly curved anteriorly, umbones prominent and rounded, umbonal 

 ridge angular, and extends to the margin of the shell ; anterior end rounded, 

 posterior acutely angular ; surface marked by numerous fine concentric lines 



Venus D'Orbignyanus, pi. 3, fig\ 2. Shell inequilateral, somewhat 

 convex, beaks small and inclined anteriorly, umbones large and rounded ; 

 cardinal margin curved; anterior end rounded, posterior subangular ; surface 

 marked by strong concentric lines. This species resembles, in its outline, the 

 common V. mercenaria, (M. violacea)of our coast. It differs from 

 V. Auca d'Orb. in having the cardinal margin more strongly curved, in be- 

 ing more angular posteriorly, and in not being so regularly marked on the 

 surface. 



Pinna m i n u t a, pi. 3, fig. 10. Shell small, robust, narrow ; umbonal ridge 

 subangular and nearly parallel with the cardinal line ; cardinal and basal mar- 

 gins straight ; posterior end sub-biangular ; surface marked by strong lines of 

 growth. 



Modiola cretacea, pi. 3, fig. 3. Shell small; beaks small, anterior; 

 umbonal ridge rounded, continued to the posterior basal margin, gradually 

 losing itself in the general curve of the shell, cardinal line arcuate, basal edge 

 sinuous ; surface concentrically striate. 



Anomia parva, pi. 3, fig. 15. Shell thin, orbicular, very slightly convex, 

 pearly ; beak small but acute ; surface marked by concentric undulations, 

 crossed by delicate radiating lines. 



[May, 



