272 



DISCOVERY REPORTS 



find in the same specimen one arm having the dorsal plates contiguous, and another with 

 them non-contiguous. The radial shields are, on the whole, narrower and more elongate 

 than in typical microplax, and the scaling of the disk less smooth. There are generally 

 only four arm spines, also on the proximal joints, but sometimes there are five. Size and 

 arm length is as in typical microplax. 



The tentacle scale may be wanting on some joints, particularly in the distal part of 

 the arms ; in the young specimens they are generally lacking completely. Rarely there 

 may be two scales at a single pore. 



These structural differences are of only small importance, and, as stated above, were 

 it only for these characters, there would scarcely be sufficient reason for keeping them 



Fig. 12. Amphiura microplax, var. disjuncta, n.var. Part of oral side (a) and dorsal side (b). Dorsal 

 side of arm joints from the middle of the arm (c). a, <25; b and c, <20. b, c, drawn from a larger 

 specimen than that from which Fig. a was drawn. 



separate from typical microplax. But the fact that the latter is viviparous and apparently 

 parthenogenetic — no males having been found — whereas the present form has separate 

 sexes^the males being particularly conspicuous — and is probably non-viviparous, 

 necessitates keeping it as a distinct form, though very closely related to A. microplax. 

 It seems to be the best course to designate it not as a separate species, but as a variety or 

 subspecies of microplax. 



Several of the gonads, particularly the large male gonads are found to be infested with 

 a Nematode, lying coiled up within the gonad. 



Amphiura monorima, n.sp. 



St. 27. 15. iii. 26. West Cumberland Bay, South Georgia, no m. Several specimens. 



St. 39. 25. iii. 26. East Cumberland Bay, South Georgia, 179-235 m. i specimen. 



St. 42. I. iv. 26. Off mouth of Cumberland Bay, South Georgia, 102-204 m. 4 specimens. 



St. 123. 15. xii. 26. Off mouth of Cumberland Bay, South Georgia, 250 m. 3 specimens. 



St. 140. 23. xii. 26. Stromness Harbour to Larsen Point, South Georgia, 122-136 m. 8 specimens. 



