326 DISCOVERY REPORTS 



Affinities. Although Halamchne magellanica resembles H. rosmari closely in many 

 respects, and in particular in the form of the highly specialized chelicerae, it may be 

 distinguished from H. rosmari, as well as from all other species in which the character 

 has been described, by the oval form of the genital shield and its comparatively large 

 size. From H. rosmari it may further be separated by the form of the anal plate, the 

 sternal plate, the genital slit and the sensory area of the first pair of legs in both male 

 and female. 



Habitat. This is the first record of a species of Halarachne from Otaria byronia. 

 Two species, H. zalophi, Oudemans, and H. otariae, Steding (possibly a synonym of 

 H. zalophi), are recorded from the nares of Otaria californica. 



The records of the hosts and hence of the probable distribution of some of the species 

 are of doubtful value. H. attemiata was described by Banks (1910) "from a seal pup, 

 St Paul Island". Dr Oudemans takes this to be the St Paul Island of the Southern 

 Indian Ocean, but there are two other St Paul Islands— one off the coast of Nova 

 Scotia and one in the Pribilov Islands, Bering Sea— and it seems more probable that 

 Banks was referring to one of the latter, most likely the Pribilov Islands, where there 

 is a large fur seal herd. The species H. americana, described by Banks in 1899, 

 was taken in Zoological Gardens from the branchial passages of Monachus tropicalis ; 

 but in such a case accidental infection is always possible and it is doubtful whether one 

 is justified in regarding the distribution of the host (West Indies, Coast of Yucatan to 

 Florida and Bahamas) as established for the parasite. This difficulty is further illustrated 

 in the case of H. rosmari, which was taken from the nares of a walrus sent from 

 Franz- Josef Land to Hagenbeck's Zoological Gardens in Hamburg; but in a letter to 

 Mr J. E. Hamilton Dr Hagenbeck states: " . . .the whole time before the war our 

 Walrusses and Sea Lions have always lived together in the same basin. There is con- 

 sequently every possibility of the Sea Lions' parasites having gone from those to the 

 Walrus ". One ought to add, however, that Dr Oudemans, who described the species, 

 is of opinion that since the walrus and sea lions were only together for a few months 

 "it is scarcely admissible that in such a short time the Halarachnids of Zalophns 

 should go over and propagate in the nasal cavities of Odobaefius." Until we know more 

 of the life-history and habits of the mite this question must remain doubtful. 



I wish to thank Dr Kai L. Henriksen of the Zoologiske Museum, Copenhagen, for 

 allowing me to examine specimens of Halarachne halichoeri, and Dr E. Titschack of the 

 Zoologisches Staatsinstitut und Zoologisches Museum, Hamburg, for a similar kindness 

 in lending me specimens of Halarachne rosmari. 



