TETROKCHIS. 123 



advancing growth, however, the gelatinous peduncle develops, becoming 

 very prominent in adults (PI. 29, fig. 4). The manubrium likewise grows 

 longer, until it is finally about as long as the peduncle, but as its length 

 is variable, this character is probably not of taxonomic importance. The 

 mouth opening is simple (PI. 29, fig. 6) ; but when it is closed the manu- 

 brium is folded in such a way that there appear to be four long lips 

 (PI. 29, fig. 7). The peculiar course of the radial canals on the peduncle 

 (PI. 29, figs. 6, 7) is apparently constant. 



The long, sausage-shaped gonads, well developed in the larger speci- 

 mens, hang from the canals at the apex of the bell cavity. The smallest 

 specimens show no trace of them, and they are first visible as minute 

 spherical swellings in specimens about 5 mm. high (PI. 29, fig. 10). The 

 entire subumbrella surface, as well as the velum, is very muscular. 



Color. — The Medusa is colorless except that the entodermic lining of 

 the manubrium, visible only when the distal portion of the manubrium 

 is everted (PI. 29, fig 8), is pink. 



This race is decidedly larger than A. rosea, especially at the time that the 

 gonads appear. The rather larger number of tentacles seems to separate it 

 from the previously known varieties of A. digitale. 



The present captures indicate that in the tropics Aglantha belongs to 

 the intermediate, not to the surface fauna. This is a marked divergence 

 from the northern forms, which are frequently recorded from the surface, 

 though apparently at times penetrating to a considerable depth (Guen- 

 ther, :03). Off the coast of Greenland, according to Vanhoffen ('97), the 

 young live at a depth of thirty or more metres, and rise to the surface 

 with the formation of the gonads. 



The very broad horizontal distribution of the present series from 13° S. 

 to 20° N. is also of importance, for this considerable extension northward 

 in the intermediate zone suggests a possible overlapping with A. digitate 

 var. camtschatica, which is common on the surface in the Gulf of Georgia, in 

 latitude 48° N. (A. Agassiz, '65). 



Tetrorchis, gen. nov. 



Trachynemidae without peduncle ; with four gonads attached to as many 

 radial canals near their junction with tin' ring <-<iiih/. 



This genus is established to include ;i single species, apparently new, 

 which is distinguished from all other Trachynemidae, to which family it 



