424 DISCOVERY REPORTS 



Test, usually free, but often sessile, especially in the earlier stages; irregularly 

 nautiloid in the adult form, exhibiting 89 chambers in the final convolution which 

 partly enfolds the earlier growth; dorsal side convex, very coarsely punctate, the 

 septation of the earlier chambers often obscured ; the later chambers becoming inflated, 

 and separated by sunken sutures as growth progresses, until in the last half convolution 

 the shell becomes involute. The umbilical margins of the later chambers on the dorsal 

 side are smooth and thick-walled. The ventral side is nearly flat, thick-walled, finely 

 perforate, and glassy. The umbilical region is concave on both sides, but deeper on the 

 ventral side ; the aperture is a well-marked slit extending right round the inner face of 

 the final chamber. 



The stages of growth, both of the megalospheric and microspheric forms, have been 

 identified. They present such varied aspects at different stages of growth that they 

 might easily be mistaken for distinct species. In the megalospheric forms the pro- 

 loculum is large and followed by three other chambers of equal size, the whole forming 

 a quadrate test with rounded corners, thick- walled, and coarsely punctate on the dorsal 

 side, with hardly noticeable sutural lines; on the ventral side it is thick-walled but 

 smooth or glassy, the sutures rather depressed. The aperture is a small hole on the 

 peripheral margin. In the next stage, chambers are added which rapidly increase in size 

 and height, particularly on the dorsal side, the test becoming inaequilateral. As growth 

 progresses the height of the chambers becomes more equally distributed on both dorsal 

 and ventral sides, until finally, in edge view, the peripheral margin of the first con- 

 volution disappears in the middle of the slit-like aperture of the final chamber. The 

 megalospheric form has only i^ convolutions with 8 chambers in the final convolution. 



The microspheric form appears to be rare, and no very young individuals were ob- 

 served. Balsam-mounted specimens, however, show that it commences with a very 

 minute proloculum, followed by a large number of small chambers gradually increasing 

 in size and inflation for two convolutions before entering upon the final convolution, 

 which is similar to that of the megalospheric form. There is not any noticeable difference 

 in the two adult stages. 



As with many species of Anomalina and Truncatulina , the chitinous lining is very 

 thick and dark in colour ; the chambers are thus rendered very clear on the ventral side 

 of the shell up to a considerable size. In the words of d'Orbigny : " La teinte est d'un 

 rose violace d'autant plus fonce qu'on s'eloigne de la derniere loge; le cote interne de 

 chaque loge est aussi plus fonce". 



Estimated diameter of microsphere, c-oi mm.; of megalosphere, o-o8 mm. Micro- 

 spheric young, one convolution about 0-44 mm. long; 0-36 mm. broad. Four-cham- 

 bered megalospheric young, about 0-30 mm. long; 0-25 mm. broad; 0-15 mm. thick. 

 Adult test averages about 1-20 mm. long, i-o mm. broad, 0-70 mm. thick at oral surface. 



D'Orbigny recorded the species from the Falklands as "common", and also from his 

 sounding off Cape Horn in 160 m. It is quite common at many of our stations, notably 

 WS 83, 84, 88, 91 , 93, 246, and sessile specimens in all stages of growth are of frequent 

 occurrence. 



