ASTEROIDEA 205 



ray breaks at muscular joint between first and second adambulacrals (no adambulacral 

 syzygial joints). Type, O. nutrix. 



Remarks. This genus differs from all known Brisingidae in having in each inter- 

 radius a highly specialized, axial, brood chamber, in which young are protected until 

 they attain a diameter of at least 6 mm. The number of rays, 11-14, is determined at 

 the outset of development and is not increased by later additions, as in Labidiaster. 



Odinella may be regarded as an off-shoot of Odinia stock with which it agrees in the 

 possession of papulae on both disk and rays, a single subambulacral spine, and probably 

 in the general structure of the actinostomial ring. In Odifiella there is no completely 

 syzygial joint among the proximal adambulacral plates such as is found in Brisingo, 

 Craterobrisinga, Brisingella, and Asirostephane, inter alia. It is probable that no complete 

 syzygy occurs in Odinia, notwithstanding my statement to the contrary.^ Doubt is 

 cast on the matter by a ray of Odinia magister apparently broken from the disk between 

 first and second adambulacrals. There are remnants of muscle on the proximal face of 

 what I take to be the second adambulacral. The succeeding joints are muscular ones 

 except possibly the upper part of the second-to-third. I do not have adequate material 

 to examine this question in other species of Odinia. 



No known Brisingid has a genital region as concentrated as that of Odinella. On this 

 basal inflation of the ray are numerous dorsolateral spines, some of which grow fast to the 

 opposite body wall, locking together, in gravid males and females, all the genital regions 

 into a sort of circular accessory disk, bristling with spines longer than those of the disk 

 proper. As a special adaptation this contrivance undoubtedly prevents loss of rays which 

 have at best a flimsy attachment to the disk. In the female these spine-bridges, as well 

 as the numerous interdigitating but free spines, form a basket work which effectively 

 confines the eggs and developing young to the brood chambers, into which fresh water is 

 driven by cilia. The functional part of the arm for locomotion and trapping of Crustacea 

 (by means of the pedicellariae) is restricted to the flexible region distal to the genital 

 inflation. 



In Odinia, the sides of the proximal part of ray between the skeletal arches is provided 

 with numerous stout plates in a close irregular mesh. The arches are rather poorly 

 defined near disk. Very numerous papulae occur on the sides as well as dorsal surface of 

 the genital inflation, which extends along ray, for 9 or 10 well-spaced arches and reaches 

 its greatest size at about its middle, not anywhere close to disk. In O. magister the male 

 gonad opens near base of ray (as in Odinella) either in the first or second intercostal area 

 which are here heavily plated and diflicult to distinguish from the primary arches. 



Brisingaster de Loriol, which strongly suggests Odinia except that the intercostal 

 plates are embryonic and there are no papulae, differs from both Odinella and Odinia 

 also in having gonads in a series of 8 or 9 proximally just above the adambulacral plates. 

 There appears to be a syzygy between first and second adambulacral plates. Throughout 

 the genital area of 9 or 10 well-spaced complete arches, the subambulacral spine has a 

 modified expanded truncate tip. First pair of adambulacral plates (and sometimes most 



1 Fisher, 1919, p. 501 : 1928, p. 4. 



DXX 18 



