396 THE VOYAGE OF H.M.S. CHALLENGER. 
above. Further, these plates “are large and well-developed in the adult forms in 
Pentagonaster semilunatus, Gymnasteria carinifera, in various species of Pentaceros, 
and a large number of the Goniasteride.” 
It thus appears that a small number of Ophiurids and a larger number of Starfishes 
have two rings of plates between the radials and the dorsocentral, Just as is the case in 
Marsupites; though in the majority of the members of both groups there is only one 
ring, the elements of which are interradial, as is the case in all the Urchins, so far as 
is yet known. The homology of these interradial plates with the basals of the Penta- 
crinoid larva and of Marsupites is a part of Lovén’s theory; while he long ago pointed 
out the homology between the central abactinal plate of the Starfish larva and the dorso- 
central of Marsupites.' I do not see therefore, how he can do. otherwise than accept 
the views of Sladen and myself respecting the homology of the radial plates immediately 
surrounding the dorsocentral of Ophiomusium, Amphiura, Asterias, and Zoroaster with 
the under-basals of Marsupites. In both cases these radial plates separate the dorso- 
central from an interradial series which are called basals in a Crinoid and genitals in 
an Urchin or Starfish, z.e., the plates for which Lovén proposes the general name of 
“costals.” Ido not imagine that he will deny (1) that the radial plates between the 
costals and dorsocentral of Marsupites are homologous with the radial plates between 
the costals and dorsocentral of the young Asterias; nor (2) that these radial plates are 
homologous with the under-basals of Cyathocrinus, which are immediately within the 
basals, or as he prefers to call them, costals. But, according to his present view, these 
under-basals of Cyathocrinus represent the dorsocentral of the young Asterias. There 
is, however, no reason to seek for the homologue of the five under-basals of a dicyclic 
Crinoid in the single dorsocentral of a larval Starfish; for this dorsocentral is 
surrounded by five plates which correspond exactly in their relative positions with 
the under-basals of Marsupites, and therefore of other dicyclic Crinoids, including 
Cyathocrinus. 
If I may be permitted to use here an expression employed by Prof. Lovén with respect 
to another homology which he establishes, I would say that ‘‘ to anyone believing in the 
consistency of Nature’s ways, there is no reason whatever for doubting” that the apical 
systems of some Asterids and Ophiurids contain plates which are truly homologous with the 
under-basals of a Crinoid. It is unfortunate that their presence was not discovered in 
time to be noticed by Prof. Lovén in his recent discussion of the question; for I am 
sanguine enough to believe that it would have led him to reconsider his views respecting 
the homology of the five under-basals of a Crinoid with the primitively single dorso- 
central of a Starfish. 
The interradial plates in the apical system of a Starfish or Urchin are usually known 
as the genitals; but this term, ‘‘ besides being expressive of incidental relations peculiar 
1 Etudes, loc. cit., pp. 72, 86. 
