10 THE VOYAGE OF 1 1. M.S. CHALLENGER. 



Pectyllis, 1 Haeckel, 1879. 



Trachynemidse with eight genitalia in the course of the eight radial canals, without 

 centripetal canals. The genitalia are cut in two by eight radial mesogonia or leaf-shaped 

 mesenterial bands, and connected with the bases of the stomach. Oral cavity without 

 oral funnels, and without side pouches. Tentacles with sucking-cups very numerous 

 and placed closely one over the other in several rows on the umbrella margin. Numerous 

 (8 or 16 ?) auditory clubs. 



The genus Pectyllis, with the two following genera Pedis and Pectantlris, form the 

 special small group of the Pectyllidse, which I placed in the System der Medusen 

 (1879, p. 265) as a sub-family in the family of the Trachynernidae. The Pectyllidse are, 

 however, so strongly distinguished by several striking peculiarities from the remaining 

 Trachynernidae, the Marmanemidse, that it is better to separate them as a special family. 

 The Pectyllidas agree with the Marmanemidse in having eight radial canals and eight 

 genitalia hanging from them, in the form of the depressed umbrella, and in the absence 

 of a gelatinous gastral peduncle ; on the other hand, they are distinguished from them by 

 two peculiar characteristics which are wanting in the other Trachornedusse, in having eight 

 mesogonia and numerous sucking-tentacles furnished with terminal sucking-cups. The 

 auditory clubs of the umbrella margin are free as in the Aglauridae, not enclosed in 

 "marginal vesicles" as in the Marmanemidse. The peculiar "mesogonia," or genital 

 mesenteries, are thin, membranous, vertically-placed leaves, which extend in the radial 

 plane between the central oesophagus on the one side and the eight sac-shaped repro- 

 ductive glands on the other, are inserted in the middle line of the latter, and sometimes 

 pass along the radial canals almost to the umbrella margin. The upper part of the umbrella 

 cavity is, therefore, divided into eight radial sections (" infundibula subumbralia "). 

 The peculiar sucking tentacles of the Pectyllidse are hollow or solid, very elastic and 

 contractile threads, which bear a powerful sucking-cup at the free end, and are used for 

 adhering by suction. Part of them resemble the " ambulacral-feet " of the echinoderms 

 in form and in the mode of motion. The sucking tentacles are very numerous in all 

 three genera of the Pectyllidse, sometimes closely packed together in several rows, one 

 above the other, on the margin of the umbrella ; sometimes grouped more or less distinctly 

 in separate bunches ; in all of them we can distinguish sixteen (or 32 to 64) bunches more 

 or less divided by marginal incisions, so that the umbrella margin appears almost lobed. 

 A further peculiarity of the Pectyllidse is the extremely broad, powerful velum, which 

 apparently, in all three genera, can be extended till, like a sphincter, it completely closes 

 the umbrella cavity ; they surpass all other Craspedotse in this extreme development 

 of the velum. The Pectyllidse are finally distinguished by a peculiar formation of the 



1 ILjxTvAAi?, Pectyllis, derivative of Pedis. 



