294 REPORT OF NATIONAL MUSEUM, 1897. 



BILOCULINA RINGENS Lamarck. 

 (Plate 39, fig. 2.) 



A stout, inflated, smooth, and polished shell, slightly compressed 

 from above downward, nearly circular in outline when seen from above, 

 the final segment projecting well beyond the preceding one, to which it 

 is smoothly and firmly joined; aperture usually a broad slit with a 

 nearly equally broad valvular lower lip. Diameter, 1.5 mm. (-fa inch), 

 more or less. Longitudinal section shows arrangement of chambers 

 characteristic of the genus, and the apertures alternately at opposite 

 ends of the shell. 



Localities. Off Cape Hatteras and in the Gulf of Mexico (stations 

 2115, 2352, 2385), 460 to 840 fathoms. 



BILOCULINA COMATA Brady. 

 (Plate 39, fig. 3.) 



Subglobular in form, otherwise like B. ringens ; characterized specific- 

 ally by surface ornamentation consisting of more or less conspicuous, 

 fine, straight, parallel stria3 covering the whole shell; aperture an 

 arched slit, with a broad, thick valvular lower .lip. 



Locality. West coast of Cuba (station 2352), 463 fathoms. 



BILOCULINA ELONGATA d'Orbigny. 

 (Plate 39, fig. 4. ) 



Like B. ringens except that it is long oval in contour. The typical 

 specimens are small, but there is constant variation both in size and 

 breadth of oval. 



Localities. Gulf of Mexico and the North Atlantic (stations 2383, 

 2385, 2584), 500 to 1,200 fathoms. 



BILOCULINA DEPRESSA d'Orbigny. 

 (Plate 40, fig. 1.) 



Smooth, compressed, round; margin thin and sharp: aperture usu- 

 ally a long, narrow slit, with a valvular lower lip thinner and less 

 prominent than in B. ringens ; rarely the aperture is contracted to a 

 nearly circular orifice. Longitudinal section shows the conformation 

 and arrangement of the chambers. 



Localities. Gulf of Mexico and off Marthas Vineyard (stations 2374, 

 2378, 2568, 2570), 26 to 1,830 fathoms. 



BILOCULINA DEPRESSA, var. SERRATA Brady. 

 (Plate 40, fig. 2.) 



Identical in general characters with B. depressa, but having the edge 

 dentate, with more or less closely set teeth. The penultimate segment 

 often shows the serrations more conspicuously than the final one. 



