292 ' ENDEAVOUR SCIENTIFIC RESULTS. 



Acanthella, like Acanthocladium among the Statoplea, is 

 distinguished only by having its upper hydrocladia abortive, 

 and terminating in, or replaced by, pointed spines. 



Heteroplon is a synonym for those species of Plumularia 

 in which the anterior mesial sarcothecse are rigid instead of 

 freely moveable, a condition which, as I pointed out long 

 ago, is as common as the contrary. It may, of course, be 

 held that this character is sufficient to found a genus upon 

 (though the difference between the fixed and the moveable 

 sarcotheca depends merely on the thickness of the basal part, 

 and every intergradation occurs) ; no one, however, has 

 adopted the genus since Allman, and it is only mentioned 

 here since it appears in Stechow's recent list of the genera. 

 Even Allman, when proposing the genus, at the same time 

 described as a Plumularia (P. laxa) the common P. campanula, 

 which has similar sarcothecse to H. pluma. If Allman's 

 figure of the latter species in front view 1 be compared with 

 my front view of P. campanula? it will be seen that the 

 anterior sarcothecse are as similar as if copied from the same 

 individual. Allman also describes as P. armata a species 

 which, according to Billard, has sarcothecse of the same 

 type, though differently represented in Allman's figure. 



Of course the admission of the rigid sarcotheca as a good 

 generic character would involve, for those who admit the 

 genus Antennella, the creation of a new genus for those 

 unbranched forms having moveable anterior sarcothecse (the 

 type form, A. secundaria, having them fixed), and similarly 

 the genus Monotheca of Nutting would have to be subdivided, 

 since of about eight forms known to me five have the anterior 

 .sarcothecae moveable, while three have them in the form of 

 .stout rigid processes of the internode. 



Halopteris is another type with fixed sarcothecse, but its 

 -chief peculiarity was supposed to be the possession by the 

 lateral sarcothecse of a long tubular stem, adnate to the 

 hydro theca. In 1887 I suggested that this was probably 

 only a peduncle, or process from the internode, differing only 

 in its greater length from those found in P. catharina, P. 

 campanula, and many other species. Nutting has confirmed 

 this surmise in regard to Allman's species, and I have 

 specimens of a nearly allied form P. balei, Bartlett which 

 seems exactly similar to H. carinata so far as the lateral 

 sarcothecae are concerned, and in this the structures in 

 question are also undoubtedly peduncles. Antennella balei, 



1. Allman Rep. Sci. Results "Challenger" Exped., Zool., vii., 

 Hydroida, pt. I., 1883, pi. viii., fig. 2. 



3. Bale Proc. Linn. Soc. N.S. Wales, (2), III., 1888, pi. xx., fig. 2. 



