io6 DISCOVERY REPORTS 



contains the proloculum followed by one piano-spiral convolution of minute biserial 

 chambers regularly increasing in size, the axis of the spiral being at right angles to the 

 main axis of the shell. 



The megalospheric form predominates everywhere, sometimes to the entire exclusion 

 of the microspheric. Its appearance is very distinctive, especially in young specimens, 

 where the proloculum shows like a glassy bubble on the ventral side of the bulbous top. 

 As the shell develops, it becomes less noticeable owing to the deposition of secondary 

 shell matter. The pair of chambers immediately following the proloculum are com- 

 pressed in shape, owing to their position on the dorsal side behind the proloculum. 

 After them the chambers are regularly arranged biserially. Average specimens exhibit 

 four to five pairs of chambers, but several specimens having as many as seven to eight 

 pairs have been seen. 



The microspheric form is easily distinguished by its narrower initial end, which is 

 rather wedge-shaped than bulbous. Owing to the thickness of the wall, the internal 

 structure is difficult to determine, but, as previously stated, the very small proloculum is 

 followed by a piano-spiral coil of minute biserial chambers (probably four to five 

 pairs), regularly increasing in size, and followed by a further series of six to eight 

 pairs of straight chambers. The microspheric form thus attains a greater average 

 length than the megalospheric, the other dimensions remaining much the same. 



An average megalospheric specimen measures about 070 mm. in length by 0-30 mm. 

 in greatest breadth and 0-25 mm. in thickness. One very large specimen attained 

 I -08 mm. in length. The megalosphere as measured in optical section (internal) 

 averages o-i mm. in diameter. 



Microspheric specimens average about 0-90 mm. in length by 0-35 mm. in greatest 

 width and 0-30 mm. in thickness. A large specimen attained 1-35 mm. in length. The 

 microsphere could not be measured with any certainty, owing to the thickness of the 

 shell. It is certainly very minute. 



E. crassa is a very abnormal type, and until its relationships were definitely established 

 by the discovery of the microspheric form with its coiled initial portion, its systematic 

 position remained uncertain. Its nearest ally is unquestionably E. pupa (d'Orbigny), 

 from which it differs in many points, notably in the marked development of the produced 

 series of chambers and their regular Bolivine arrangement. E. pupa was first described 

 by d'Orbigny from the Falkland Islands, and it is one of the most abundant and 

 variable species in the Discovery collections from that area. None of the variations, 

 however, approaches E. crassa, which does not occur at all in the Falkland area, but 

 is relatively common in South Georgia and adjacent waters, and, so far as our present 

 knowledge goes, is almost confined to that area, where it constitutes one of the most 

 characteristic local species. Presumably the two species, E. pupa and E. crassa, are de- 

 rivatives from a common ancestor which inhabited both areas. 



I have little to add to the information already published and quoted above. E. 

 crassa is certainly the most typical if not the commonest species round South Georgia, 

 occurring in greater or less abundance at more than half of all the stations examined. 



