ball: mollusca and brachiopoda. 371 



conspicuously as two whitish disks on the umbones, smooth and easily eroded ; 

 beaks subcentral, touching, not recurved ; lunule and escutcheon large for the 

 size of the shell, with no radial markings and faintly delimited but not distinctly 

 impressed; ligament not visible externally; posterior dorsal slope straight, poste- 

 rior end shorter and somewhat pointed ; anterior slope slightly convexly arcuate, 

 anterior end rounded ; base very convexly arcuate ; concentric sculpture only of a 

 few irregularly distributed impressed lines indicating resting stages ; radial sculp- 

 ture of numerous very fine, slightly raised, close-set lines, with equal and regu- 

 larly spaced interspaces, covering the disk ; interior pearly, smooth, with entire 

 valve margins, muscular scars distinct ; hinge line with six posterior and ten 

 anterior teeth, the two series separated by a deep pit containing the nearly 

 vertical chondrophore. Lon. 5.0; alt. 4.5; diam. 3.0 mm. 



U. S. S. *' Albatross," station 4656, off the coast of Peru in S. Lat. 6°55' and 

 W. Lon. 83° 34', in 2222 fathoms, green mud, bottom temperature 35°2 F. 

 U. S. N. Mus. 110,572 ; station 2792, off Mauta, Ecuador, in 401 fathoms, mud, 

 temperature 42°.9; and station 3418, off Acapulco, Mexico, in 660 fathoms, sand, 

 temperature 39°. 



This is an exceedingly elegant little shell with a wide range in latitude and 

 depth. 



Nucula declivis Hinds. 



Nucula declivis Hinds, P. Z. S. London, 1843, p. 97 ; Zool. Voy. Sulph., 1844, 

 Moll, p. 63, pi. 18, fig. 8. 



U. S. S. " Albatross," station 2805, Panama Bay, in 51 fathoms, mud. Also at 

 station 2778, in Magellan Straits, in 61 fathoms, sand, bottom temperature 

 47°.9 F. U. S. N. Mus. 110,685. 



The locality of this species is not given by Hinds, but his excellent figure and 

 brief description agree well with the shell above referred to, and as his collections 

 were largely made on the Pacific coast of south and middle America it is probable 

 that the identification is correct. 



Nucula colombiana Dall, n. sp. 



Sliell small, very inequilateral, ovate, white with an olivaceous pale pcriostra- 

 cum, smooth, brilliantly polished, anterior dorsal margin and base convexly 

 arcuate; posterior dorsal margin short, straight, subtruncate, with the valve- 

 margins pouting a little in the middle of the flattened posterior area ; posterior 

 end attenuated, short, almost pointed ; anterior end evenly rounded ; beaks 

 turgid, opisthogyrate ; interior pearly, with smooth margins to the valves ; 

 posterior hinge line with seven, anterior with fourteen teeth, separated by a well- 

 developed chondropliore. Length of whole shell, 4.5; of posterior segment, 1.0; 

 alt. 3.0 ; max. diam. 2.2 mm. 



