82 DISCOVERY REPORTS 



Genus Ammomarginulina, Wiesner, 1931 



122. Ammomarginulina ensis, Wiesner (Plate III, figs. 1-4). 

 Ammomarginulina ensis, Wiesner, 193 1, FDSE, p. 97, pi. xii, fig. 147. 

 Two stations: WS 199, 334. 



Test free, much compressed, especially in the early stage which is planospiral, rather 

 loosely coiled, and contains about two convolutions, the last convolution containing 

 nine to ten narrow chambers. These are followed by a straight series of chambers, 

 four to seven in number, narrow and compressed at first, tending to become more 

 inflated towards the aperture, which is central in the early stages, sometimes becoming 

 slightly produced and marginal in the adult form. Sutural lines curved butvery indistinct, 

 the chambers being difficult to distinguish except in balsam-mounted specimens. Con- 

 structed of rather large mineral grains firmly agglutinated, but without much visible 

 cement; surface rather rough, colour pale straw to golden yellow. 



Length, about 0-4 mm. ; breadth at spiral portion ranging between 0-2 and 0-3 mm. ; 

 breadth of uniserial portion ranging between o-i and 0-15 mm. 



Many specimens occur at WS 334 at a depth of 3705 m. This station is well to the 

 north of South Georgia, and the absence of the species at stations intermediate between 

 WS 334 and 199, which is far to the south, near the South Orkney Islands, is rather 

 remarkable. Only a single specimen was noted at WS 199 at a depth of 3813 m., but 

 the species, though never common, is of very constant occurrence in the deep water 

 Antarctic material. 



I had already described this species in MS. under the name Ammobacidites ensis 

 before I became aware of Wiesner's prior publication (^ut supra). Wiesner has created a 

 new genus Ammomarginulina, of which this is the genotype. The characteristic feature of 

 the genus is the position of the aperture, which is on the outer marginal edge, as in 

 Margimilina. I had not attributed so much importance to this feature, though the 

 general resemblance of the form to MarginuWia ensis, Reuss, had, by a coincidence, 

 caused me to select the same specific name as Wiesner. His definitions of the new genus 

 and species are brief, but sufficient in connection with his figure drawn from a trans- 

 parent specimen for identification with my specimens. He writes of the genus Ammo- 

 marginulina: "The sandy shell is spirally coiled at first, later chambers arranged in a 

 straight line, sutures curved, aperture on the back edge ". Of the species it is stated that 

 "it bears the features of the genus. The shell wall is built up of flat mica-like mineral 

 flakes with little cement ". No dimensions, locality or frequency are given, but from the 

 figure his specimen agrees in size with ours. As Wiesner's material was from the opposite 

 side of the Antarctic area, the species is apparently universally distributed over the 

 Antarctic seas. 



