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



Among: the Actinia? with degenerate tentacles. I described in my former Challenger 

 Report a new species, in which the extent of retrogression of the tentacles can be 

 recognised in a degree attained by no other form. I was compelled to dispense with a 

 detailed description of its structure, since the only specimen at my disposal was on 

 the one hand much mangled, and on the other rendered so brittle by preservation in 

 chromic, acid that it could not be methodically investigated. I am glad to be in a 

 position to fill up the deficiency by means of two specimens found in the supplementary 

 material, both well preserved, although considerably altered in shape by violent con- 

 traction. In both cases, as in the example previously described, the stomatodaeum is 

 so much evaginated as to take the place usually occupied by the oral disc, the latter 

 falling outwards from this point like a body-wall (PI. I. fig. 13). On the other hand, 

 pedal disc and body-wall are alike deeply retracted on the lower side. The body-wall 

 forms a cup like the shell of a Patella, the pedal disc projecting into the cup somewhat 

 like the body of the Patella. In so marked a de-formation, dimensions can with 

 difficulty be given, and can serve only for approximate orientation. In the larger of 

 the two specimens (from 120 fathoms at Station 305a), the pedal disc had a diameter 

 of about 2 cm., the distance between the edge of the oral disc and the mouth reached 

 2 - 5 cm. ; the length of the stomatodseum was at most places l - 5 cm., and at the 

 siphonogiyphes more than 2 cm. The corresponding dimensions of the smaller 

 example (Station 147 ; depth, 1G00 fath.) are essentially less, — diameter of pedal disc, 

 0'07 cm. ; radius of oral disc, T2 cm. ; length of the stomatodseum, TO cm. From the 

 nature of the contraction may be inferred that in both cases the dimensions of oral 

 disc and stomatodaeum are excessive, as the result of evagination, while those of the 

 pedal disc are too small. 



On the pedal disc are about 160 radial furrows, of which, however, only a 

 proportion reach the centre, the rest dying out sooner or later. The ridges between 

 the furrows are somewhat toothed, in the manner formerly described by me as occurring 

 in Polyst&midium and Polysiphonia. In the centre of the pedal disc lies a pit about 

 the size of a pin's head, which cannot be proved to be an opening. 



On the exterior of the body-wall also, similar ridges, alternating with furrows, 

 run longitudinally from pedal to oral disc ; their number is greater, being close on 400 ; 

 they differ in size, some few of less considerable development rising between every two 

 of the stronger ridges. At the edge of the oral disc they all pass into a strong circular 

 ridge, which forms the sharp boundary between body-wall and oral disc. 



The pedal disc and body-wall possess on their inner surfaces the circular muscle- 

 fibre layer occurring in all Actinias ; on the body-wall this is strongly pleated, and the 

 more so, the nearer we approach to the upper edge. In the immediate neighbourhood 

 of the edge the pleating is so marked that one may term it a sphincter ; it causes here 

 the circular ridge mentioned above as occurring at the upper edge of the body-wall 



