HYDROMEDUSAE, SIPHONOPHORES, AND CTENOPHORES. 287 



Niobia is included by Mayer in his " tribe Bythotiaridi," but its 

 swollen tentacle bases argue against this view. Maas (1910, p. 7) 

 suspects that it is a Leptomedusa. 



Genus HETEROTIARA Maas 1905. 



The genus was proposed by Maas (1905) for two immature speci- 

 mens named by him II. anonyma. It has since been recorded by me 

 (1909a) for two more examples of anonyma from the eastern Pacific, 

 for large series of that species from the northwest Pacific (1913) and 

 from the Western Atlantic (1918), and by Vanhoffen (1911) for one 

 anonyma and four specimens of a new species, minor, from the 

 " Valdivia " collection. The present collection contains eight ex- 

 • amples of minor, which are in such good condition that they allow me 

 to amplify the original account of that species somewhat. 



Vanhoffen (1911) has questioned whether the eastern Pacific speci- 

 mens which I referred to anonyma really belonged to that species, on 

 the ground that his examples, as well as those of the Siboga, 19 mm. 

 high, had only eight tentacles and no sign of others in process of 

 formation, whereas mine, only slightly larger (22 mm.) had eleven 

 or twelve. But the northwest Pacific specimens (1913, p. 26) showed 

 that the number of tentacles varies (7-10) independent of size (13-21 

 mm. high), besides varying in number from quadrant to quadrant of 

 the bell margin. Hence, as I have pointed out (1913), there is no 

 real separation between the eastern Pacific and the other recorded 

 specimens of anonyma. And this same conclusion has been reached 

 by Hartlaub (1913, p. 351). 



H. minor is distinguished from H. anonyma by its small size and 

 by having about twice as many tentacles. Data are now available 

 from enough specimens to establish the constancy of the difference, 

 and consequently the validity of Vanhoffen's species. It is possible 

 that the Tiara prismatica of Maas (1893) belongs to one or other 

 of these two species. But in the absence of any figure of the entire 

 Medusa, this must remain doubtful (Hartlaub, 1913, p. 349). 



HETEROTIARA MINOR Vanhoffen. 



Plate 39, fig. 9 ; plate 40, figs. 2-4. 

 Heterotiara minor Vanhoffen, 1911, p. 212, figs. 8a, 8b. 

 Heterotiara minor — material examined. 



