TRACHYMEDUS.« — HALICREAS. 



391 



characters, for specimens displaying such characters in intermediate degrees must either be 

 placed in a third "genus" or confusedly classed either with one or the other, sometimes being 

 considered to belong to one and again to the other genus. It is well known that in Haeckel's 

 system certain medusae, by merely contracting or extending the manubrium, may change^from 

 one "genus" to another, while his Siphonophorae invariably break up into new "genera" and 

 "species" when the sexual generation is set free. 



Vanhoffen distinguishes five species of Halicreas + " Haliscera," the specific distinctions 

 being based on form of bell, width of radial-canals, position of gonads, and color. Maas, 

 1905-06, shows that the form of the bell is very variable in H. papillosum, and he believes that 

 certain of Vanhoffen's species should be reduced. 



Halicreas resembles the Trachymedusae in its marginal tentacles and 8 simple radial- 

 canals with a marginal ring-canal. It recalls the Narcomedusae, however, in its conical- 

 cylindrical stomach with its wide, round mouth-opening. 



Maas made a restudy of the Valdivia specimens and has concluded that the Antarctic 



Haliscera alba Vanhoffen belongs to the genus Homceonema Maas and is closely related to 



the Arctic medusa Homceonema platygonon Maas. Maas does not redescribe the medusa 



and his grounds for this opinion are not wholly clear. I have, therefore, retained H. alba 



provisionally in the genus Halicreas. "Isonema" racovitzar, described from a single preserved 



specimen by Maas, appears to have all of the characters of Halicreas. As the generic name 



Halicreas takes precedence, I do not think we can follow Bigelow, 1909, in calling this genus 



Homceonema. 



Halicreas papillosum Vanhoffen. 



(?) Halicreas minimum, Fewkes, 1882, Bull. Mus. Comp. Zool. at Harvard College, vol. 9, No. 8, p. 306. 



Halicreas papillosum, Vanhoffen, 1902, Wissen. Ergeb. deutsch. Tiefsee Expedition, Dampfer Valdivia, Bd. 3, Lfg. I, p. 68, 

 taf. 9, fign. 7, 8; taf. II, fig. 30. — Maas, 1905, Craspedoten Medusen der Siboga Expedition, Monog. 10, p. 57, taf. 10, 

 fig. 70; taf. 11, fig. 71.— Bigelow, H. B., 1909, Mem. Museum Comp. Zool. at Harvard College, vol. 37, P- ! 3 8 > p' at es 

 3. 33. 34- 



2+3- 



Fig. 142.— Halicreas papillosum. Fig. 244.— Halicreas (Haliscera) rotundalum. 



Fig. 243.— Halicreas papillosum. Fig. 245.— Halicreas glabrum. 



Above figures after Vanhoffen, in Tiefsee Expedition Valdivia. 



