MUSEUM OF COMPARATIVE ZOOLOGY. 33 



The position of the newly formed interambulacrals as regards the 

 terminal is similar in Asterina and Asterias.* In Asterina, from Lud- 

 •wig's diagram, I should judge that these plates arise near the outer 

 ends of each pair of ambulacral rafters, so that a line through them 

 would pass through the length of the rafter. In Asterias, however, 

 the interambulacrals arise in the interval between the outer ends of the 

 early formed ambulacral rafters. 



Plates homologous to the under basals of Criuoids are recognized by 

 Sladen f in several species and genera of Asteroids, including Asterias 

 rubens and A. glacialis. I have been struck in the examination of 

 figures of deep-sea starfishes to see how close, in some instances, the 

 likeness between the test of certain of them and that of the young Aste- 

 rias is. The young and adult of Zoroaster seem closely to resemble cer- 

 tain young stages of Asterias. Sladen comments on the " unmistakable 

 crinoidal facies " which the young Zoroaster has, and regards a young 

 stage of this Asterid as highly suggestive of the Ophiuroid genus Ophio- 

 pyrgus. "Whether the resemblance between the young Asterias and the 

 young Zoroaster can also be interpreted as a crinoidal facies, I leave to 

 those more familiar with the Crinoids to consider. The simple arrange- 

 ment of plates in Zoroaster is an embryonic feature. 



There is some danger in affixing to the plates of starfishes names of 

 plates which are current among students of Crinoids. While it may be 

 held to be proper to do so, if the Crinoids .represent the ancestral con- 

 dition of Echinoderms, it might lead to error if they are simply special- 

 ized or degenerate descendants of other and older groups. 



posed them " Unpaare Interambulacralplatte." It is thought that he means by 

 the latter the marginal plates. 



* Fig. 97, Plate VII., of Ludwig's paper on Asterina would seem, from the po- 

 sition of the terminal as regards the feeler, F, to be a view from the abactinal side. 

 Such a conclusion is likewise supported by the relative position of the plates, A 2 , 

 or second pair of ambulacral rafters. If, however, the view from which the figure 

 is seen is from the abactinal side, it would seem as if other abactinal plates would 

 be represented. If they were figures of Asterias of the same age, such plates cer- 

 tainly might be expected to be visible. Perhaps the term " bei tieferer Einstel- 

 lung " explains the peculiar arrangement of plates and the loss of the abactinals. 

 I am unable to understand the figure, since the view is said to be from a prepara- 

 tion (fig. 96) which is shown from the actinal side. 



t On the Homologies of the Primary Larval Plates in the Test of Brachiate 

 Echinoderms. Quart. Journ. Micros. Science, Vol. XXIV., new ser., 1884. 



Judging from Sladen's figure of Zoroaster fulgens (fig. 16), it seems that what he 

 calls the " underbasal " is also represented in the abactinal hemisome of a young 

 Asterias. 



VOL. xvii. — no. 1. 3 



