REPORT ON THE SIPHONOPHOR^E. 297 



a phylogenetic point of view, represent the older and simpler forms of Auronectse. They 

 resemble the Circalida? in many respects (PL XXI. figs. 1-4) ; and especially the mono- 

 gastric Auronula (PI. VII. fig. 50) may be compared to Circalia. This latter, however, 

 possesses no trace of the aurophore. The central axial canal of the Stephalidae (PI. VII. 

 fig. 40, ca) and its distal mouth (ao) are of special interest, as comparable on one hand 

 with the terminal protosiphon in the basal cormidium of the Physalidse, and on the other 

 hand with the central sterile siphon of the Disconectse. By the thickening of its wall, and 

 the development of anastomosing nutritive canals in this, arises the characteristic trunk 

 of the Auronectse. Its terminal mouth remains permanently open in the Stephalidse. 



Synopsis of the Genera of Stephalidse. 



Corona of neetophores simple. All tentacles simple, of the same size and form, . . 62«. Stephalia. 



Corona of neetophores double or multiple. A corona of proximal tentacles, annulated, much 



larger than the simple distal tentacles, . . . . . .626. Stephonalia. 



Genus 62a. Stephalia, 1 Haeckel, 1888. 

 Stephalia, Hkl., System der Siphonophoren, p. 43. 



Definition. — Stephalidae with a simple corona of neetophores, arranged in a single 

 circle. Tentacles simple, all of the same form and equal size. 



The genus Stephalia (PI. VII.) is the simplest and oldest (phylogenetically) among 

 the four different genera of Auronectse which I have examined. Its corona of neeto- 

 phores is simple, as in Auralia and Circalia (PI. XXI. figs. 1-4), all the neetophores 

 being placed in one horizontal plane. The tentacles are simple, cylindrical, not annulated 

 filaments, all of equal size and similar form. The gonodendra (PL VII. fig. 49), which, 

 however, in the specimens examined were not fully developed, are smaller than in 

 Stephonalia, and seem to want the large gonopalpon characteristic of that genus. 



Stephalia corona, n. sp. (PL VII.). 



Habitat. — North Atlantic, in the depth of the eastern Gulf Stream.  

 Fseroe Channel and Shetland Islands, August 22 and 24, 1882 ; depth, 640 and 516 

 fathoms (" Triton " Expedition, Dr. John Murray). 



Corm. — Four different specimens of this interesting species were examined by me, 

 all preserved in rather good condition. One of the corms (fig. 39, in profile; fig. 40, in 



1 Stephalia — Sea-ring, orstpos, akios. 

 (ZOOL. CHALL. EXP. — PART LXXVII. — 1888.) Hhhh 38 



