HYDROZOA RITCHIE. 



865 



a fragment from Station 47. Only 11 cm. of the stem remains, 

 but its basal diameter is 9-5 mm. ; of its two primary branches 

 the only complete one is 300 mm. long, while a secondary branch 

 is 125 mm. 



There is little to be added to Bale's (1888) excellent descrip- 

 tion of the minute chaiacters of the trophosome. The branches 

 arise from the hydrocladiate tube of the colony, which is anterior, 

 and have several simple internodes with solitary hydrothecae, 

 before a hydroclatle-bearing internode is reached. In the hydro- 

 theca itself there occurs an undescribed knot of chitiu, varying 

 considerably in prominence as seen in lateral aspect, which juts 

 into the hydrotheca cavity from the abcauline wall, very near to 

 the bottom of the cup. The margin of the hydrotheca varies 

 considerably, the characteristic broad lateral lobe especially 

 ■exhibiting stages of decrease in size, so that in some specimens 

 it has become almost obsolete. 



Gonosome. — The corbidse are of great length, up to 10 mm., 

 and a little over 1 mm. in diameter. Those which I have seen 

 are closed, except for a space between the bases of the leaflets 

 such as Bale has described. Here, however, the margins of the 

 leaflets frequently rise into very pronounced crests, bordered on 

 the outer edge by about ten sarcothecse, and rising so far above 

 the bod}' of the corbula that the inner edge also becomes free 

 and is supplied with three or four sarcothecse. The short lateral 

 spur which projects outwards and forwards from the stalk of 

 each leaflet is also better developed, for here it has become an 

 accessory leaflet armed with up to seven sarcothecfe. The general 

 structure of the body of the corbula is that of a cylinder encased 

 within a cylinder, the inner cavity containing the reproductive 

 bodies, the space between the two cylinders (formed of the two 

 walls of the corbula leaflets), containing ccenosarc which is in 

 free communication with the exterior through the sarcothecae. 



Dimensions. — 



Organs. 



Hydroclade -bearing internode, length .. 

 ,, ,, diameter 



Hydrothecate internode, length 



Hydrotheca, depth 



,, diameter at mouth 



Hydroclade, length 



Corbula, length 



,, diameter 



Typical form. 



0-36 mm. 



0-29 ,, 



-.32-0 -41 mm. 



0-27-0-34 ,, 



0-18 



up to 13 ,, 



up to 10 ,, 



about 1 ,, 



Variety from 

 Station 55. 



■25-0-32 mm. 



0-38-0 -42 ,, 



0-31-0-34 ,, 



0-29-0-31 ,, 



0-21 



up to 13 ,, 



A variety occurs at Station 55 in which the hydroclades are 

 more closely set ; the hydroclade internodes, and therefore the 



