26 HYDROIDA II 



best exposition of the family is that given by Kramp, who has in two works (1911 and 1913) given 

 a close description, which as regards its main features, is adhered to in the present work. Kramp 

 (1913 p. 14) inclines to the view that the family should be divided into two, a primitive family, Cus- 

 ptdelhdtf, where the closing apparatus is formed by the upper part of the hydrotheca wall, and a more 

 highly developed family, Campanulinida, where the closing apparatus consists of the original roof of 

 the hydrotheca. Kr amp's point of view is doubtless highly correct, but as my material is not suited 

 to serve as basis for more detailed exposition, I have merely noted the two mentioned groups as sub- 

 families, otherwise following mainly the generic division established by Kramp (1911 p. 383). 



The gonothecse in several members of the family are of considerable interest, differing only in 

 their greater dimensions from the hydrothecse - - doubtless a primitive feature. This peculiarity is 

 known among the genera of Stegopoma, Cuspidetta, and Lafoeina. Unfortunately, very little is known 

 as to the gonophores, but we know that the family comprises the polyp-generation of a number of 

 highly heterogeneous Leptomedusse, which are distributed by systematists throughout a whole series 

 of families. As, however, the polyps, save for the mentioned characters in the sub-families, exhibit 

 very considerable uniformity, we can hardly, from what we know at present, consent to a further sub- 

 division of the family. We have evidently here to deal with a series of biological divergencies in the 

 medusa generation, particularly calculated to demonstrate the impossibility of establishing, in the pre- 

 sent state of our knowledge, any common system for the two generations. The hydroid system cannot 

 here be adapted to the^ medusa system, which evidently demands thorough investigation of the biolog- 

 ical adaptation phenomena in order to give a system which can claim to be considered as fairly 

 satisfactory from a phylogenetic point of view. 



Sub-family Cuspidellinae. 



Campanulinida with closing apparatus formed by the integrating distal part of the hydro- 

 theca wall. 



Gen. Stegopoma Levinsen. 



Colony creeping or developed to an upright rhizocaulome. The hydrothecae tubular to narrow 

 bell-shaped, without diaphragm; the closing apparatus consists of two folding membranous parts of the 

 distal hydrotheca wall, which shuts down in a roof-shaped lid over the aperture, between two diame- 

 trally opposite teeth. The polyps have uniform gastral endoderm. 



Stegopoma plicatile (M. Sars) Levinsen. 



1863 Lafoea plicatilis, M. Sars, Bemserkninger over fire norske Hydroider, p. 31. 

 1874 Calycclla plicatilis, G. O. Sars, Bidrag til Kundskaben om Norges Hydroider, p. 95. 

 1893 Stegopoma plicatile, Levinsen, Meduser, Ctenophorer og Hydroider, p. 37. 

 1893 caricum, Levinsen, p. 37. 



