A COLLECTIOX OF HYDROIDS. 299 



adnate for one-half to two-thirds of its length to hydrocanlus. 

 Adcauline free surface smooth. The margin has four small 

 equidistant teeth, of which the lateral pair are perhaps the 

 best developed; there is an operculum of four flaps, two 

 adcauline and two abcauline. Below the margin there are 

 three internal knobs of chitin, two adcauline {acl.l-.) and one 

 on the opposite surface [ah.k.). 



In the specimen from Park Rynie {B) the hydrotheca is 

 sunk in the hydrocanlus to a less extent than in that from 

 Bird Island (C). 



The adcauline free surface of the hydrotheca is swollen, 

 especially in the specimen from Bird Island, and it is perfectly 

 smooth and not transversely I'idged as in S. gayi. 



Length 0'59 mm., greatest breadth 0*28 mm. 



Hydranth. — Badly preserved, perhaps about 28 tentacles. 



Gonosome. — The gonangia are known only from the Park 

 Rynie specimen (text-fig. 6, B). The male gonangium is ovate, 

 with a short tubular neck and three short apical teeth. Over 

 the distal half there are about seven transverse rug•^e ; the 

 proximal half is smooth. 



Total length about 2-08 nun., breadth 0*87 mm. ; thickness 

 of perisarc 28 u. 



Systematic Position. — According to Professor Nutting 

 S. gayi has not been found in the Pacific Ocean, and it is 

 noAv a question whether the differences between the present 

 hydroid and gayi are sufficient to Avarrant the formation of a 

 new species. The only marked differences are : the complete 

 absence of rugae on the hydrotheca, and the amount to which 

 the hydrotheca is sunk in the hydrocanlus. In S. gayi not 

 more than one-half of the hydrotheca is adnate to the hvdro- 

 caulus, while in the hydroid from Bird Island two-thirds are 

 generally adnate. This last character, however, is certainly 

 variable, especially if there is justification in considering the 

 specimens from Bird Island and Park Eynie as belonging to 

 the same species (text-fig. 6, cf. B and C). 



Only by a series of observations on the variability of 

 S. gayi, Avith respect to the rugas on the hydrotheca, would it 



VOL. 1, PART 3, 22 



