367 Costa Rica Miocene — Olsson 95 



The Ancillaria pinguis Guppy, from Jamaica is probably a 

 closely related species. Guppy' s figure in the Geological Maga- 

 zine, vol. I, Decade 2, is very poor and insufficient. Our shell 

 seems to differ by its much longer spire and more slender shell. 



The Ancillaria chipolana Dall, figured on Plate 41, fig. 3, of 

 the Wagner Institute, is larger and has a longer spire. No um- 

 bilical pit is shown in the figure. 



Gatun Stage: Water Cay, {Isla de Aqua). 



Genus MARGINELLA Lamarck 



Marginella MacDonaldi Dall Plate 6, figures 14, 15, 17, 19 



Marginella MacDonaldi Dall, 1912, Smith, Misc. Coll., vol. 59, No. 

 2, p. 7. 



This large Margi^iella is one of the most common and char- 

 acteristic species of the Gatun beds of Costa Rica. It is extreme- 

 ly valiable in size and general from and heaviness of its shell, as 

 may be seen in the accompanying figures of the more common 

 varieties. 



T5^pically the shell is oblong-cylindrical with a small spire of 

 about 4 whorls, usually completely covered in front by a broad 

 mass of callus, which spreads over the whole base of the shell 

 and the outer lip, leaving an elevated ridge along each side as 

 frequently seen in Cyprcea. From the back, the spire maj'- be 

 seen lying in the mass of callus. 



The Marginella mindiensis Cossmann is a smaller related 

 species from the Canal Zone. It differs also in having its outer 

 lip finely denticulated, while in MacDonaldi the outer lip is us- 

 ually smooth. 



Length 28, diameter of base 15, vertical diameter 10 mm. 



24 14 9 mm. 



25 13 9.5 mm. 

 17.5 II 7.5mm. 



Gatun Stage: Banana River. 



