HYDROIDA. BALE. 261 



S. huttoni, both of which have the hydrothecal margin with 

 6-7 teeth, and if they possess an operculum I am most 

 inclined to think that it consists of as many valves as there 

 are teeth. In either case these two species cannot be referred 

 to any of the hitherto described genera." It may also be 

 observed that in Stechow's recent summary of the genera 

 no place is found for S. elongata or its allies. It will 

 probably be conceded therefore that there is justification 

 for the establishment of a genus for such species as are 

 excluded from the Sertulariidse (as restricted) by the absence 

 of an operculum, while the conspicuous denticulation of the 

 hydrotheca-margin distinguishes them, if less decisively, from 

 the genus Synthecium. If such a genus be not admitted the 

 only alternative would seem to be the modification of the 

 latter genus to make it include these forms. 



According to Stechow's arrangement the family Synthecidse 

 comprises three genera Lytoscyphus, Synthecium and Hypo- 

 pyxis. I believe that the latter genus is erroneously asso- 

 ciated with the Synthecidse, as I have pointed out in discussing 

 H. distans. 1 The genus now proposed will take its place 

 beside Synthecium, and, as will be shown further on, there 

 are not wanting signs of a connection between them more 

 intimate than would be supposed at first sight. 



It must be recognised that some of the forms which I now 

 refer to Levinsenia have not been sufficiently examined to 

 make it certain that they never develop an operculum, but 

 some undoubtedly do not, and the others sufficiently resemble 

 them to warrant their association pending fuller examination. 



Besides the two species mentioned by Levinsen, S. 

 elongata and S. huttoni I assign to Levinsenia S. pluridentata 

 (Kirchenpauer), S. insignis Thompson, S. acanthostoma Bale, 

 S. crenata Bale, along with the species described by Billard 

 as possibly a sexual form of S. elongata, and which may in 

 the meantime be described as S. billardi. z Of these S. elongata 

 is most widely known, and it has been examined by several 

 observers, who have not in any case noted the presence of 

 an operculum. I have a beautifully mounted specimen, 

 stained, and with the hydranths expanded as in life, and I 

 cannot detect any trace of an opercular structure. Billard 

 says nothing as to the presence or absence of an operculum 

 in the form described by him. S. acanthostoma has been 

 studied histologically by Warren, who says that there is 

 not a trace of operculum. I believe this i. the only member 



1. Bale Biological Results "Endeavour," ii., 4, 1914, p. 107. 



2. Billard Ann. Sci. Nat., Zool., (9), xi., 1910, p. 22, fig. 8. 



