52 HYDROIDA II 



stalked and mobile, or small, rudimentary or entirely effaced, being represented merely bv holes in 

 the periderm, at times with slightly raised, asymmetrical edges. The margin of the hydrotheca is 

 almost always without teeth. The colonies are monopodial with terminal growth point. The gastral endo- 

 derm of the polyp is divided into a fore stomach and a digestive stomach part, the limit between them 

 appearing as a constriction round the body of the polyp. 



As thus defined, the family covers the group Eleutheroplea auctt. but it also further includes 

 such primitive forms as Kirckenpaueria, which lacks true sarcothecre. What have been taken for such 

 are in reality merely low, as a rule somewhat asymmetrically developed margins round the aperture 

 in the periderm through which the sarcostyle passes out. This formation cannot be altogether regarded 

 as a parallel to the sarcotheca, which forms the fixed point of support for the sarcostyle, and is as a 

 rule furnished with a diaphragm in Plumulariidce. 



On the other hand, it must be admitted that there are certain transition forms which render 

 the limit between Plumulariidee and Aglaopheniidce somewhat indistinct at times, as we find species 

 with both stalked mobile, and immobile, sessile sarcotheca;; these forms must be regarded as primitive 

 Aglaopheniidce. Such transition forms are also met with as against Haleciidcr, though it has not in 

 this case been found advisable to unite the two families. We find, as a matter of fact, in almost every 

 hydroid family such intermediate forms, the position of which is more or less a matter of doubt. If 

 entirely definite boundary lines had to be drawn, it would very possibly involve the reduction of the 

 entire group of hydroids to one or two families. But the heterogeneity would then be too great. In 

 the same way, the Plumulariida, as viewed by Nutting (1900) and Stechow (1913) make a too 

 heterogeneous group, which as both writers also admit, really comprises two very well defined main 

 groups. As these two main groups differ in principle, as much as any two families in the other 

 family series of thecaphore hydroids, and as, moreover, the intermediate forms here are neither more 

 numerous nor more marked than elsewhere, it will be correct to keep the two groups apart as sepa- 

 rate families. 



Gen. Kirchenpaueria (Jickeli). 



Upright pinnate colonies, the stem bearing on its apophyses only undivided branches (hydro- 

 cladia) with several hydrothecse, these being unilaterally arranged, and fused with the branch. Beside 

 the nutritive polyps appear the sarcostyles, which proceed from holes in the periderm; these holes are 

 often surrounded by a slightly raised, as a rule somewhat asymmetrically developed periderm collar. 

 Paired sarcostyles lacking. 



Bedot (1916) reintroduces this genus, and defines it further in such a manner that the old 

 Sertularia pinnata Linne appears as its typical species. 



In the list published in 1915, "Nomina conservanda. Unter Mitwirkung zahlreicher Spezialisten 

 herausgegeben von Prof. C. Apstein" tSitzungsberichte der Gesellschaft naturforschender Freunde, 

 Berlin, Mai 1915) we find under polyps (p. 126—127) as type for Plumularia the Plumularia pinnata 

 L. This is well calculated to show that a list such as the one mentioned may easily manage to 

 defeat its own ends. Within the very large number of species which are referred to the genus Plu- 

 mularia, the Plumularia pinnata takes up a quite exceptional position, owing to its reduced sarcothecae, 



