128 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL.8 



Remarks. — I have ventured to transfer Semper's Tkyone chilcnsis to 

 this genus, as his description of that unusual form agrees exactly with the 

 numerous specimens I have had occasion to examine, and the species 

 differs distinctly from Pattalus mollis Selenka, of which I have likewise 

 had the opportunity to study a long series. My results are in complete 

 agreement with Ludwig's conclusions, that Lampert's species is a syno- 

 nym of Semper's Thy one chilensis (and probably some or all of his 

 Pattalus mollis). But contrary to Semper's and Theel's belief, the num- 

 ber of tentacles is constant in this species. 



The inner circle of tentacles is often completely withdrawn so that 

 only the 10 larger ones are visible. The inner tentacles become quite stout 

 with advancing age but remain, nevertheless, always distinctly smaller 

 than the external ones, and the inner circle is well separated from the 

 outer one. The radials, as Semper describes them, are slipper shaped, al- 

 most rectangular, broadest posteriorly with a large depression below the 

 attachment for the retractors ; the interradials are small in the young indi- 

 viduals; in the older they are completely concealed in the thick tissue, and 

 the calcareous ring appears to be composed of 5 stout radials. Semper 

 noticed only one tuft of small accessory stone canals but may possibly 

 have failed to examine both sides of the mesentery. The Polian vesicles 

 are distinctly arranged in tufts, and most of them are branched. 



Except for the presence of end plate and a few rosettes in the tentacles, 

 spicules are so rare that they often are difficult to find. Semper figures a 

 few branching rods perforated by a few holes, and such spicules have been 

 found. 



The color is strikingly different from that of Pattalus mollis even in 

 preserved individuals. It is mottled gray, sometimes almost black on the 

 dorsal side, with paler ventral side and black tentacles. In freshly col- 

 lected individuals the tube feet may have a reddish tinge, possibly caused 

 by the hemoglobin contained in the water vascular sj^stem. The skin seems 

 never to contain a reddish pigment as Pattalus mollis, nor does it ever 

 fade to that uniform dull reddish brown which is so characteristic of 

 Selenka's species. 



Athyonidium chilensis seems to be the most common phyllophorid 

 known from Chile. On the coast of Peru it is often known to occur in the 

 same localities as Pattalus mollis, but buried in sand with the tentacle 

 crown expanded on the surface, while the former clings to the rocks 

 (H. L. Clark's observations). 



