296 REPORT OF NATIONAL MUSEUM, 1897. 



SPIROLOCULINA ROBUSTA Brady. 



(Plate 42, fig. 1.) 



Much compressed laterally, broad -oval to nearly round, more or less 

 concave on both sides; extremities angular or pointed; periphery 

 rounded, with sharp, projecting marginal angles, which are often 

 toothed. Four to six segments visible on both sides, outlined by the 

 acute prominent marginal angles; aperture round, with a T-shaped val- 

 vular tooth in the protruding end of the final segment. Longitudinal 

 and transverse sections show the arrangement of chambers character- 

 istic of the genus. 



Locality.— Gulf of Mexico (stations 2383, 2399), 200 to 1,200 fathoms. 



SPIROLOCULINA ROBUSTA, series. 

 (Plate 42, fig. 2.) 



This is a series, selected from material dredged at a single station, to 

 show an apparent evolution of Spiroloculina robusta from Biloculina 

 depressa. The specimens are shown in pairs, the first of the pair being 

 a whole shell resting upon its side, the other being a transverse section 

 of a similar shell standing on end. The few specimens exhibited show 

 a passage from one form to the other by well-defined steps, but with a 

 large number of specimens the gradation is so easy that it becomes 

 indefinable. The series illustrates the difficulties of classification in 

 this order of animals. 



Locality. — Gulf of Mexico (station 2377), 210 fathoms. 



SPIROLOCULINA EXCAVATA d'Orbigny. 

 (Plate 41. fig. 5.) 



Small, much compressed, long oval with projecting ends, very con- 

 cave, showing the minute early segments; margins broad and rounded. 



T,nra.l.i.t/ti "NY»r. rppnvrlprl 



Locality. — Not recorded 



SPIROLOCULINA NITIDA d'Orbigny. 

 (Plate II, fig. 4.) 



More or less broadly oval, flat, thin, small; the segments inflated, 

 without angles, the final one projecting at the oral end. Long diameter, 

 about 0.75 mm. {-£$ inch). 



Locality. — Collected in the Gulf of Tokyo. 



SPIROLOCULINA LIMBATA d'Orbigny. 

 (Plate 12, fig. 3.) 



Thin, flat, broad oval, with slightly projecting ends and square mar- 

 gin ; segments numerous; sutures marked by prominent, smooth ridges. 

 Length, about 0.75 mm. ( 3 \r inch). 



