32i Dominican Fossils— Maury 157 



strong, sharp-edged, curved, radial plications; aperture oblique, 

 receding below, sagittate, the outer lip being produced into a 

 very conspicuous point ; the cord-like umbilical callus is continu- 

 ous with the thickening of the margin of the lip and descends into 

 the umbilicus. This species has a general resemblance to the 

 Floridian Pliocene T. calliglyptum Dall and to the recent D. 

 Schumoi Vanatta from the British Honduras. Greatest diameter 

 4 mm. 



This rare and curiously beautiful shell is named as a tribute 

 to the memory of Dr. Orville A. Derby, lately Director of the 

 Servico Geologico do Brazil, who for over two score years knew of 

 no sacrifice too great to advance the knowledge of the palaeontol- 

 ogy of his adopted land. 



Locality. — (Exp'd '16) Bluff 3, Cercado de Mao. (A sin- 

 gle shell). 



Genus Fissuridea Swainson 



Fissuridea He?ieke?ii, n. sp. 

 Plate 24, Figure 21 



Shell resembling F. alternata Say but differing in the orna- 

 mentation, the concentric laminae being raised into hollow vault- 

 ed scales and tubes as they cross the radiating ribs. An exam- 

 ination of many specimens of F. alternata shows some shells have 

 crenulated scales but none show the hollow tubular structure 

 characteristic of the fossil shell. As in F. alternata every fourth 

 rib is stronger; the perforation is in front of the middle of the 

 shell, and is keyhole-shaped; the anterior slope is slightly convex, 

 the posterior slope slightly concave. Length 19, breadth 12, al- 

 titude 7 mm. 



Dedicated to the memory of Colonel Heneken, who made the 

 first collection of fossils and the first sections of the Tertiary 

 formations of the Rio Yaqui. 



Locality. — (Exp'd '16) Zone H, Rio Cana at Caimito. 

 (A single shell.) 



Fissuridea alternata Say 

 Plate 24, Figure 22 

 Fissurella alternata Say, Jour. Acad. Nat. Sci. Phila., 1st ser. vol. 2, 



