GEPHYREA. 1 73 



allowing the entrance of the ccelomic fluid extend the tentacle. A.s far as I could 

 make out, the tentacles arise from a ring and not from a horseshoe, and the mouth is 

 in the centre of the ring. 



Behind the bases of the tentacles were little projections of the epidermis hearing 

 thickened, cuticular projections (fig. 10). These morphologically resemble hooks, but 

 no part of the tip is bent over, and the whole structure is something like a blunt 

 speardiead. They are undoubtedly the homologues of the hooks in other unarmed 

 Gephyrea, and in structure they fairly closely resemble the processes called " hooks" 

 in Sipunculus amtralis, the only member of the genus Sipunculus which has "hooks." 

 The spear-head projections were apparently arranged in rings, but with the some- 

 what broken sections, obliquely cut, it was not possible to definitely make out how 

 many rings there were. Figure fO also shows the very prominent papillae of the 

 posterior part of the introvert the outer layer in the figure the continuous layer of 

 muscles, the nervous system cut twice, and the almost completed fusion of the 

 retractor muscles around the base of the head. 



Part of the brain is shown in section in figure 9, which has been cut through the 

 pigmented, concave layer of cells which forms the eye. 



Genus : Centrosiphon, n. g. 



The new genus may be characterized as follows : Sipunculoids with circular 

 anterior and circular posterior thickened, chitinoid shields; the introvert emerges 

 from the anterior shield in the centre, and is not inclined to one side more than to 

 any other, it is quite central ; both shields are separated from the side walls of the 

 cylindrical animal by a prominent ridge ; the papillse are very prominent on the 

 introvert, and on it and the anterior shield they are uniformly scattered, on the 

 posterior shield they are in radiating hues ; anteriorly and just behind the mouth are 

 rows of spear-head-shaped chitinized projections obviously homologous with the hooks 

 of other species. 



Species: Centrosiphon herdmani, u. g. et sp., Plate I., figs. 4, 5, 6, 7, 8, i) and 10. 



With only two specimens at one's disposal, and those of the same species, to 

 attempt to pick out the specific characters partakes of the nature of prophecy, but, 

 judging by other and allied Gephyrea, the following, or some of them, will probably 

 rank as specific characters : Longitudinal muscles in a continuous sheath ; four 

 retractor muscles, of these the ventral are very thick and inserted about a quarter of 

 the animal's length behind the anterior shield, and the dorsal are very slim and 

 inserted one on either side of the anus, a very little way behind the anterior shield ; 

 the nephridia are rather dorsal in position and open close to the edge of the dorsal 

 shield; the tentacles are few in number, some twelve or fifteen, and probablv 

 surround the mouth as a simple ring; eyes well developed ; no calcareous deposits on 

 either shield. 



