Aiisti'til i(vn Hi/drald.s. 145 



//. arcuatd is imuli laijirr and has the ed^'es turned outwards and 

 recurved till it dftni appears (|uitr tulmlai-. The lateral teeth, how- 

 ever, arc the most distinctive. There are normally three on each 

 side; in //. /is</(/ioi(fes the middle one is always the largest (or at 

 least as large as either of the others), and is always more or less 

 everted, as are also the fii-st and third. In //. arcuata, on the con- 

 trary, the middle tooth is the smallest, and is incurved, while the 

 first and third are everted. Tn both species the lateral teeth may be 

 reduced to two on each side, but in //. areiiatn this results from the 

 gradual disappearance of the incurved middle tooth, in //. 

 ascif/in/des it is always the third tooth which becomes obsolete. In 

 all the Austialian species of the ancidio/des-gvomp the rule -holds 

 good that tlie middle lateral tooth is the principal one; in some 

 cases the first may become obsolete, in" others the third, and in others 

 again lioth the first aTid third, but the middle one is in every species- 

 well developed, and always everted. The obsolescence of the middle 

 tooth in //. arena fa becomes more pronounced towards the ends of 

 the hydrocladia, but I do not find this to be the case with the 

 decrease of the third tooth in H. ascidioides, the hydrothecae near 

 the ends often having the teeth best developed. 



The mesial sarcothecae of H. arcuata. differ from those of H. 

 ascidioides by tlie more erect proximal portion, the much more 

 pronounced tapering of the free portion, and the closed pointed 

 ends. I have never seen the ends closed in H. ascidioides, except 

 in certain deformed specimens, where they were bluntly rounded. 

 The lateral sai-cothecae of H. ascidioides are never, so far as I 

 have seen, prolonged into long closed horns as in H. arcuata, though 

 as in many other species the tubular mouth is considerably elon- 

 gated towards the ends of the hydrocladia. Only on the proximal 

 part of the hydrocladia in //. arcuata are the little circular orifices^ 

 equally developed, the lower ones become progressively more and 

 more prominent towards the ends of the hydrocladia, where they 

 attain the condition of rather long open tubes, oi- even pointed 

 horns. In either case they have a lateral orifice on the inner side, 

 and the upper of the two circular orifices has disappeared. 



I have figured H. ascidioides along with H . arcuata for com- 

 parison. fSee plate XIIT). 



H.\LIfORNARIA SUPERB.A. Bale. 



Af/laopJieiiia superha. Bale, Journ. Micr. Soc. Vict., ii.,. 



1881, p. .31, 45, pi. xiii.. fig. 4-4b. 

 Halicornari^i auperha. Bale. Aust. Hydi-. Zooph.. 1884, p. 



4: id.. Proc. Rov. Soc. 



