126 THE VOYAGE OF H.M.S. CHALLENGER. 



Huxley gave an accurate description of the only nectophore observed of these four 

 " Diphyidae" ; he supposed (as did also his predecessors) that the second nectophore had 

 been accidentally lost ; it does not, however, exist at all. The genus Sphaaronectes was 

 rightly regarded by Huxley as the type of a peculiar family — Sphaaronectidae. 



During my residence in the Canary Island of Lanzerote (December 1866 to February 

 1867), I observed four different species of Monophyidae, viz.: — 



(1) Monophyes hydrorrhoa. 



(2) Mitrophyes peltifera (PI. XXVIII.). 



(3) Muggisea pyramidalis. 



(4) Cymba crystallus. 



I was able to examine the complete metagenesis of the latter species, and the develop- 

 ment of its Eudoxia, Cuboides crystallus (Pis. XLL, XLIL). 



A Mediterranean species of Sphasronectes, very similar to the Australian form dis- 

 covered by Huxley, was described in 1874 by Claus, aud called Monophyes gracilis (70, 

 pi. iv.). He observed the development of its Eudoxia, which was formerly described by 

 Gegenbaur as Diplophysa inermis (7, Taf. xvi. fig. 3). Another Mediterranean Mono- 

 phyid described by him, Monophyes irregularis, may remain the type of this genus. 

 Claus replaced the term Sphaeronectidae of Huxley by the name Monophyidae, which was 

 accepted as more significant, in opposition to Diphyidae. 



The metagenesis of the two Mediterranean Monophyidae was afterwards very accu- 

 rately examined by Chun (86-88). Compare his memoirs also for the history of this family. 



During my voyage through the Indian Ocean (November 1881 and March 1882) and 

 in Ceylon, I had the opportunity of examining some very interesting new forms of Mono- 

 phyidae and their development, viz., Monophyes princeps and Cymbonectes huxleyi 

 (PL XX VII.). Supported by these observations, and by some specimens found in the 

 Challenger collection, I was able to give the following description of Monophyidae. 



Nectophore. — The single nectocalyx of the Monophyidae exhibits differences in form 

 and structure similar to the first or proximal of the Diphyidae. Accordingly, I divide 

 the family Monophyidae into two subfamilies ; the first of these, Sphaeronectidae, has a 

 smooth hemispherical or mitriform nectophore, without sharp edges, and is allied to the 

 Prayidae among the Diphyidae, The second subfamily, Cymbonectidae, has a pyramidal 

 nectophore with five prominent edges, and is nearly allied to the Diphyopsidae and 

 Abylidae. The single nectophore of the Monophyidae is relatively large, of a bilateral and 

 quadriradial fundamental form, sometimes symmetrical, at other times asymmetrical. 

 The first nectophore of their larva is replaced by a permanent, often heteromorphous, 

 swimming-bell. 



Hydrcecium. — Since the single nectocalyx of the Monophyidae corresponds to the 

 first apical or proximal nectophore of the Diphyidae, it possesses a hydrcecium for the 

 reception of the retiring siphosome. This is an open hydroecial groove, protected by 



