Australian Hydroids. 301 



^lide of //. hexactinella sent to me by Mr. Wliit^legge, who first 

 observed it, two hydraiiths out of seven possessed five tentacles 

 only. Sexual products were apparently not observed. 



I have seen only the two usual forms of neQiatocysts in such 

 Hydras as I have examined, but I should hesitate, in the absence of 

 iuU series of sections, to decide that no others were present, as 

 the intermediate types appear much less common, and more likely, 

 from their delicate structure, to be overlooked. In the specimens 

 of H. hexactinella I find the large form in two distinct sizes, 

 averaging respectively about 13/a and 10/x in length, both sizes 

 being very abundant, while intermediate ones are very rare. In 

 £ome sections of the common species which I have seen the large 

 nematocysts measured about 15/x. 



Judging from Mr. Whitelegge's specimens I have no doubt that 

 II. hexactinella is one of the ** stalked " forms, and I think that 

 Von Lendenfeld was mistaken in stating the length of the tentacles, 

 when fully extended, as only 5 mm., or one-third ithe length of the 

 body. Ihe figure shows the body very long and slendiar, and the 

 tentacles short, but the case is probably similar to that of H. 

 orientalis, of which Annandale says that when the body is very 

 nmch elongated, the tentacles are never fully extended. 



EXPLANATION OF PLATES. 



Plate XVI. 



Pig. 1. — Ophiodes australis, n.sp. 

 Fig. 2. — Serfularella rentoni Bartlett. 

 Fig. 3. — Sertularia McCalluml (Bartlett). 

 Pig. 4. — Sertularia McCallumi (Bartlett). 

 Pig. 5. — Sertularella diayhana (AUman). 



x40. 



Plate XVII. 

 Pig. 1. — Vlumularia rotunda Mulder and Trebilcock. 

 Fig. 2. — Phtmnlaria everta Mulder and Trebilcock. 

 Pig. 3. — Plnnudaria cornufatissitna Mulder and Trebilcock. 

 Fig. 4. — riuinuhiria scahra Lamarck. 

 Fig. 5. — Phtmularia scahra Lamarck. 

 Fig. 6. — Plumularia halei Bartlett. 

 Fig. 7. — AffhiopJienia haleri, n. sp. 

 Fig. 8. — Affhiopheiiia hakeri, n. sp. 



X 80. 



