940 



THE VOYAGE OF H.M.S. CHALLENGER. 



Syjiojisis of the Genera of Stephanida. 



L Subfamily 



Lithocircida. 

 TSo typical basal feet on • 

 the base of the ring (no 

 cortinar feet). 



II. Subfamily 



Cortinida. 

 Three or four typical basal 

 feet on the ring (cortinar 

 feet). 



Eing diphragmatic or 

 amphithect; dorsal and 

 ventral bow equal. 



King smooth or thorny, with- 

 out branched spines. 



Ring armed with branched 

 spines, 



f Eing smooth or thorny, with- 

 Eing dipleuric, bilateral ; | out branched spines, 

 dorsal and ventral bow - 



different. 



Eing armed with branched 

 spines. 



Three basal feet (and an / One caudal and two lateral 



apical horn). ( feet, 



Four basal feet (and an ( Two sagittal and two lateral 



apical horn). ( feet, 



401. Archidrcus. 



402. Lithocircus. 



403. ZygocirciLS. 



404. Dendrocircus. 



405. Cortina. 



406. Stephanium. 



Subfamily 1. Lithocircida, Haeckel. 

 Definition. — S tephanida without typical basal feet or cortuiar feet. 



Genus 401. Archidrcus^' n. gen. 



Definition. — S tephanida with a simple amphithect or diphragmatic ring, smooth 

 or thorny, without branched spines and basal feet. 



The genus Archidrcus is the most primitive and simplest form of all S t e p h o i d e a, 

 and probably the common ancestral form, not only of this suborder, but of the greater 

 number of all Nassellaria (compare above, p. 893). The skeleton consists only of a 

 quite simple sagittal ring, in which commonly a slight difference of both poles of the 

 main axis (basal and apical pole) is visible, but no diflference between the dorsal and the 

 ventral bow of the ring. In my Prodromus (1881, p. 447) the species oi Archidrcus 

 were disposed partly in the subgenus Monostejihus, partly in the genus Lithocircus. 



Subgenus 1. Monostephus, Haeckel, 1881, Prodromus, j). 447. 

 Definition. — Ring circular, elliptical, or ovate, without prominent corners. 



1. Archidrcus princeps, n. sp. 



Gate circular. Eing circular, smooth, its transverse section also circular. The simplest form of 

 all S 1 6 p h oi d e a. 



Dimemions. — Diameter of the gate 0-05 to Q-QS ; thickness of the ring 0-006 to O'OOS. 

 Edbitat. — Central Pacific, Stations 265 to 274, depth 2350 to 2925 fathoms. 



1 ylrc/ticifcus = Primordial ring; ifx'i "■'Z'^og. 



