REPORT ON THE ACTINIARIA. 63 



LiPONEMiD^, Hertwig. 



Hexactinise with numerous perfect septa and witli marginal tentacles transformed by 

 retrosade formation into short tubes or into stomidia. 



Among the Actiniae of the Challenger material there were some forms in which the 

 tentacles had undergone a greater or less degree of retrograde formation. One part of 

 these, i.e., all the true hexamerous Actiniae, I have united in the family of the Liponemidse. 

 I shall discuss the others afterwards in the tribe of the Paractinise, as they are distinguished 

 from the Liponemidaj by the principle of arrangement of the septa, and I attach more 

 importance to this characteristic than even to the peculiar constitution of the tentacles. 



If this retrograde formation of the tentacles is therefore to be regarded as a j)rocess 

 which is carried on repeatedly and independently, the question may justly be raised if it 

 would not be advisable to distribute the Actinise without tentacles among the other families. 

 In this case the genus Polysix)honia ought to be placed among the Paractidse, the genus 

 Pohjstomidium among the Antheadse, as the former has a mesodermal circular muscle, 

 and the latter a weak endodermal circular muscle. 



Polysiphonia. n. gen. 



Liponemidse with tentacles, transformed by retrograde formation into short tubes 

 with wide terminal mouths ; circular muscle mesodermal, slightly developed. 



In the genus PolysifJionia we find the first stage of the retrograde formation 

 of the tentacles ; they have become short, stifi"-walled tubes, which have only a 

 weak set of muscles, are, at any rate, only capable of a small amount of contraction, and 

 are therefore of no great value, either for groping about or for seizing upon prey. But as 

 the terminal opening is very much enlarged and appears to remain permanently open, 

 they have become inhaling tubes, through which the animal can draw in water and 

 the nourishment suspended in it. 



Polysiphonia tuberosa, n. sp. (PI. II. figs. 7-9 ; PI. VI. fig. 3 ; PI. IX. figs. 1-10). 



Body stifi" and thick-walled, shaped like a stemless chalice, the surface beset with 

 roundish knobs ; oral disk, twelve lobed; tentacle tubes thickened to a swelling at the base, 

 of different sizes, placed in two alternating rows ; the larger tentacles correspond to the 

 archings inwards, the smaller to the archings outwards of the oral disk. 



Habitat.— Station 235. June 4, 1875. Lat. 34° 7'N., long. 138° 0' E. Depth, 565 

 fathoms. Twenty specimens. 



Dimensions. — Diameter of the pedal disk, 3-4 cm. ; diameter of the oral disk, 8-10 

 cm. ; height, 5-8 cm. 



Numerous specimens of a beautiful large Actinia, Polysiphonia tuberosa, were all 

 dredged on the same spot from the bottom of the sea, at a depth of 565 fathoms. To 

 judge from the nature of the material, part of them had been placed at once in spirit, part 



