72 BULLETIN : MUSEUM OF COMPARATIVE ZOOLOGY. 



rower and the pedicels distinctly biserial at the base of the ray, as they 

 are in Labidiaster throughout ; the general appearance of the ambulacra 

 in Heliaster is thus more like Labidiaster than it is like Pycnopodia. The 

 buccal membrane and the mouth parts are essentially alike in all three 

 genera, while the adambulacral armature shows no close similarity be- 

 tween either two. The pedicellariae are alike in all three, but those of 

 Heliaster (Plate 7, figs. 2-5), while somewhat more like those of Pycno- 

 podia in form, are distributed more as in Labidiaster. The digestive 

 system of the latter is more like that of Pycnopodia than it is like that 

 of Heliaster ; at least the material available to me shows no indication 

 of the five pairs of stomach-muscles, so characteristic of Asterias and of 

 Heliaster, in either Pycnopodia or Labidiaster, nor can I find any refer- 

 ence to them in the published descriptions of either genus. In the num- 

 ber of racemose glands, Heliaster and Labidiaster are alike, having a 

 large number (usually more than 15, often more than 20) without defi- 

 nite arrangement, while Pycnopodia, according to Ritter and Crocker, 

 has only 9 or 10, and these are definitely located. The discobrachial 

 wall of Heliaster is wanting in both the other genera, and even their 

 interbrachial walls are reduced to mere sheets of connective tissue with 

 little or no calcification. Were the case to rest here we should still be 

 somewhat in doubt as to whether Heliaster or Pycnopodia were the 

 nearer to Labidiaster, but there could be little question that Heliaster is 

 nearer to the latter than it is to Pycnopodia. There is, however, another 

 and very important point to be considered, and that is the location and 

 sequence of new rays, which, as we have already seen, is apparently alike 

 in Heliaster and Labidiaster, and places them in striking contrast to 

 Pycnopodia. This feature alone is sufficient to completely separate the 

 last from the others, and Viguier's opinion that Heliaster is intermediate 

 between Asterias and Labidiaster seems therefore to be justified by these 

 more recently discovered facts. Whether the latter is intermediate be- 

 tween Heliaster and the Brisingidae is somewhat less certain. The geo- 

 graphical connection between Heliaster and Labidiaster is obvious, since 

 the latter replaces the former on the southern coasts of South America, 

 but the remainder of the Brisingidae are, for the most part, widely 

 separated geographically from Labidiaster, and there is reason to believe 

 that they have originated from the Asteriidae quite independently of 

 that genus. On the whole, it looks as though Labidiaster had origi- 

 nated as an offshoot from Heliaster, living in colder and deeper water, 

 while Odinia, and perhaps Brisinga, too, are probably similarly related 

 to the genus Asterias. 



