296 REPORT OF NATIONAL MUSEUM, 1897. 



SPIROLOCULINA ROBUSTA Brady. 

 (Plat(i 42, (ig. 1.) 



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

 concave on both sides; extremities angular or pointed ; periphery 

 rounded, Avith 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, witli a T-shaped val- 

 vular tooth in the i)rotruding- end of the final segment. Longitudinal 

 and transverse sections show the arrangement of chambers character- 

 istic of the genus. 



XocaZi^^.— Gulf of Mexico (stations 2383, 2;399), 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 ISpirolocuUna robusta from BilocuUna 

 depressa. The specimens are shown in i)airs, 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.— GnU of Mexico (station 2377), 210 fatlioms. 



SPIROLOCULINA EXCAVATA d'Orbigny. 



(Plato 41, fig. 5.) 



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

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

 Locality. — Not recorded. 



SPIROLOCULINA NITIDA d'Orbigny. 

 (Plate 11, 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 42, 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^ inch). 



