28 RECORDS OF THE AUSTRALIAN MUSEUM. 



Gonosome. — The gonangial brancli replaces a hydrocladium, and bears 

 a single hydrotheca below the corbiila. The corbuhp are long and 

 cylindrical, and each consists of twelve to nineteen pairs of alternate ribs, 

 springing from separate internodes of the rachis as narrow pinnules, bnt 

 expanding aboye into broad leaflets, which unite to form a closed corbula, 

 except for oblique openings between the bases of the leaflets left by the 

 incomplete fusion of the latter in this region. Each leaflet bears a row 

 of sarcotheoie along its distal edge ; the proximal edge, howeyer, is devoid 

 of sarcothecae.i A single sarcotheca — sometimes two — occurs on the 

 I'achis at the base of each leafllet. 



Colour. — Liglit brown, stem darker. 

 Dimensions. — 



Stem internode, length 0-24-0-28 mm. 



Stem intevnode, diameter ... ... ... ... 0'28-0-35 mm. 



Hydi'ocladium, length ... ... ... ... ... up to 10 ram. 



Hydroelade internode. length ... .. ... ... 0"22-0-24 mm. 



Hydrotheca, depth ;. 0-18-0-19 mm. 



Hydrotheca, breadth at moutli- ... .. .. 010-012 mm. 



Corbula, lengtli ... ... ... ... ... ... up to 6 mm. 



Corbula, diameter ... ... ... ... .. 1mm. 



Both Billai'd and Bale have drawn attention to the tendency 

 exhibited by some species of Ai/hiophenia to reversal of the front and 

 back of the polypidom. I have observed this condition in A. hovensis, in 

 which four or five of the hydrocladia on each side alternately face the 

 front and back throughout the length of the stem, with the result that no 

 fewer than eighteen reversals occur in a length of 6 cm. A.k a 

 consequence the stem, when viewed laterally, j^i'esents a very wavy 

 appeai'ance. Billard's explanation that I'eversals followed a regenei'ation 

 of a broken part does not appear applicable in tliis instance, as I am 

 unable to detect any break in the continuity of the stem. This change of 

 front is not confined to the hydrocladia, but is shared also by the 

 corbula?. In A. hove)isix the gonangial branches replace the hydrocladia, 

 and wherever a reversal of the latter occurs the corbulfie also face in the 

 saine direction. 



Ajfi)iities.—Aijli((i/ili<'i/lti iinn-ensis is vei'v closely allied to A. sinnosa. 

 Bale-'*, from Port Denison, Queensland. It differs, however, from 

 Bale's species in the form and position of the posterior intrathecal ridge, 

 which is quite rudimentary in .1. //o»•eJ^•>/,^•, but is well developed in 

 A. sivuosa, in which species the hydropore is not elevated as in 

 A. hmvensis. Other characters by which this species may be distinguished 

 from A. sinnosa are (1) the smaller size of the hydi-otheca (0-19 mm. as 

 against 0-31 mm. in depth) ; (2) the form and position of the lateral 

 teeth on the margin ol' the hydrotheca : ()>) the difl^erent configuration of 

 the apocauline side of the liydrotheca with the mesial sarcotheca ; (4) 

 the presence on the front of the hydrotheca of a prominent external 



' Tills is contrary to Nutting's observations on the structure of the corbula? of 

 American species of Aghiophfiiia, in which there is always "a row of nematophores 

 on the proximal or inner edges of each leaf, the iKMnatophores projecting into the 

 cavity of the corbula" (Nutting— American Hvdroids. pt. I., — PlumularidiC. 1900 

 p. 33). 



- Distance from posterior wall to anterior tooth. 



3 Bale— Proc. Linn. Soc. N.S.Wales (2). iii., 1888. p. 790, pi. .\.\i.. fig. 1, 2, 



