ATLANT. DEEP-SEA EXPED. 1910. VOL. III.] 



ANTHOMEDUSAE AND LEPTOMEDUSAE. 



13 



North America: Nahant ("from July to September, quite 

 commonly", A. Agassiz), Grand Manan ("several speci- 

 mens", Fewkes), and the Gulf of Maine ("four frag- 

 mentary specimens", Bigelow).. 



Vertical Distribution. — The specimens have been 

 captured in very different depths, from about 25 to several 

 hundred meters below the surface (see above). 



The genus Halopsls was described by A. Agassiz 

 1863 and 1865 as a genus belonging to the family 

 Aequoridae and containing the species H. ocellata with 

 about 16 radial canals and H. cruciata with 4 radial 

 canals. Later authors have placed the last-mentioned 

 species within the genus Mltrocoma, thus widely separating 

 the two species. Since Bigelow (1914) has found that 

 H. ocellata has open sensory pits of the same shape as 

 in Mltrocoma, this species must also be removed from 

 the Aequoridae and placed among the Mltrocomldae. 



According to Agassiz the genus Halopsls was di- 

 stinguished from Stomobrachium Brandt by the fact that 

 the radial canals in Halopsls "take their origin in clusters 

 of three to five, radiating . . . from a large cross-shaped 

 cavity", whereas in Stomobrachium they arise singularly 

 from the periphery of the circular stomach. The speci- 

 mens taken by the "Michael Sars" and described above 

 agree in all respects with the description of Halopsls ocellata 

 A. Agassiz with the exception of the size (the European 

 specimens being somewhat smaller than the American 



specimens described by Agassiz) and the mode of origin 

 of the radial canals. It was demonstrated above, however, 

 that the canals, though separated outside the periphery 

 of the stomach, are originally grouped into four clusters 

 which are still indicated by the ciliated grooves in the 

 dorsal wall of the stomach. Also in the numerous spec- 

 imens from Grand Manan, mentioned by Fewkes (1888 

 p. 233), the radial canals arise singularly from the stomach, 

 and the same was found by Bigelow (1914) to be the 

 case in the specimens from the Gulf of Maine. — I have 

 no doubt, therefore, but that the specimens of the "Michael 

 Sars" belong to the species Halopsls ocellata Agassiz. 

 As the mode of origin of the radial canals was the 

 chief character by which Agassiz would separate the 

 genera Halopsls and Stomobrachium, and this character 

 fails, one might be inclined to think that the two genera 

 cannot be kept apart. But nothing difinitely can be stated 

 about the matter, as the two species of Stomobrachium 

 (St. lentlculare Brandt and St. tentaculatum A. Agassiz) 

 are very deficiently described, and have never been found 

 again since the original descriptions were published (Brandt 

 1835, Agassiz 1865). Neither cirri nor marginal vesicles 

 have been observed in any of the species of Stomobrachium, 

 whereas Agassiz describes the "large compound eyes" (I. 

 e. marginal vesicles) and the cirri alternating with the 

 tentacles in Halopsls. 



KRA1WP — 10 



