i62 DISCOVERY REPORTS 



Tables A and B show the difficulty of recognizing more than one variable species with the ' Discovery ' 

 material. Table A. Ancilla and magellanica forms 



Table B. Shozving variation in individuals from the same station 



If two forms require to be recognized, examples from St. 1902 and WS 776 conform with ancilla in 

 being large with three plaits and a spire ratio ranging between 1-4 and i-6. The remaining stations 

 represent the smaller magellanica form which is more slender has two plaits and a spire ratio ranging 

 between i-6 and 1-9. 



However, in the writer's opinion, such arbitrarily selected criteria lose status when other varying 

 characters are considered, such as the relative size of the protoconch and the presence or otherwise of 

 a bulging fasciole. 



It has been pointed out by Dall (1919, pp. 207-34) and others that where several embryos develop in 

 one egg capsule competition results in varying sizes in these embryos. In the New Zealand Alcithoe 

 arabica it has been noted that when a capsule develops two or more embryos they are invariably small 

 and in instances where only one persists it grows abnormally large. 



It seems that in Adelomelon ancilla a small protoconch develops into a narrow tall-spired shell with 

 a slight fasciole development and two columellar plaits, and conversely a large protoconch is associated 

 with a wider, short-spired shell, a bulging fasciole and three columella plaits. 



Dentition. Pace (1902). 



The radula is reduced to a row of tricuspid central teeth, as in most volutes. 



Adelomelon mangeri (Preston) 



Cymbiola mangeri Preston, 1901, p. 237, fig. in text. 

 Adelomelon mangeri Smith, 1942, p. 59, pi. 12, fig. 89. 



Type locality. Falkland Is. 

 Off Jetty, Port Stanley, Falkland Is., 23 Mar. 1937, 1 m. 



