LITUOLIDAE 85 



130. Turritellella laevigata, sp.n. (Plate III, figs. 5-8). 

 One station: WS 33. 



Test free, straight or irregularly curved, cylindrical, but frequently constricted at 

 irregular intervals, rounded at the proloculum, which often exceeds the maximum 

 diameter elsewhere, truncate at the oral extremity, which is slightly narrowed and bears a 

 rather large central, simple aperture. Surface smooth and highly polished owing to the 

 large amount of cement employed. Colour pale yellow, generally rather darker at the 

 aboral end. Convolutions variable in width and number, ranging up to twenty or more 

 in large individuals. 



Viewed as a transparent object under a high magnification, the test is seen to be 

 constructed of very minute mineral grains embedded in an excess of cement. The walls 

 are thin, the central columella being comparatively thick. The constrictions visible 

 externally appear to mark stages of growth ; a fresh coil is formed at the beginning of 

 each stage, the central columella being often at a slightly difl:'erent angle from the pre- 

 ceding one. The first convolution of the new coil is wider than the preceding and 

 following convolution, because it embraces the apertural end of the previous growth. 

 This gives an appearance of segmentation, but we have been unable to trace any actual 

 septum at the point of junction. All the specimens are megalospheric. 



Size up to 0-7 mm. long, o-i mm. broad. 



T. laevigata cannot be confused with T. shoneana, from which it diff'ers in the ex- 

 cessive quantity of cement employed, the external constrictions and the consequently 

 varying axis of growth. 



A good many specimens were found at WS 33 at a depth of 130 m. The species was 

 not found elsewhere in the South Georgia area but occurs also at St. 175 in the South 

 Shetlands (200 m.) and WS 482 in the same area (100 m.). See note A, Appendix, 

 p. 132. 



Genus Trochammina, Parker and Jones, i860 



131. Trochammina squamata, Jones and Parker (F 104). 

 Five stations: 145; WS 27, 33, 154, 334. 



Rare everywhere and generally small. Sessile specimens at WS 154 and 334. 



132. Trochammina rotaliformis, J. Wright (F 105). 



Two stations: 149; WS 33. 



Very rare, only one or two specimens at each station. At WS 33 the specimens are 

 very highly convex on the dorsal side. 



133. Trochammina ochracea (Williamson) (F 107). 

 Three stations: WS 41, 51 ; MS 14. 



Extremely rare. A sessile specimen at WS 51. 



8-2 



