22 The Ottawa Naturalist [May 



The single small interradial ossicle which rests against the orad 

 face of each interradial marginal will be considered as an oral. 

 The rows of ossicles which lie against the ambtdacral faces of 

 the marginals and orals will be called adambulacrals and con- 

 sidered as strictly homologous with the plates in a similar 

 position in all species of Palaeaster. They bear true cover- 

 ing plates or epineurals as do the flooring plates in the Edrio- 

 asteroidea and this terminology will therefore also correspond 

 with that used by Bather in that class. The single interradial 

 plate placed orad of each adambulacral jaw (plate III, figs. 3 

 and 4, interradius 3), will for the present be considered as homo- 

 logous with the torus angularis of the Ophiuroidea and called 

 simply the torus?. Immediately exterior to these ossicles and 

 resting on each adambulacral or primary jaw we find a pair 

 of plates which will be designated as secondary jaws. Exterior to 

 these again we find a pair of plates resting against the orad faces 

 of the interradial marginals (plate III, fig. 3, interradius 3). 

 These plates we shall call the first epineurals. So far as now 

 known the specimen shows no other ossicles save the impression 

 of a distinct terminal on radius IV (plate I, figs. 1 and 2). The 

 arm marginals, adambulacrals and epineurals have been in 

 part numbered on some of the figures presenting them. 



The marginals of this species are so characteristic that one 

 should be able to recognise its presence by them alone. Particu- 

 larly should this be true of the large interradial marginals. 

 A study of the form of the ridges and depressions on the oral 

 faces of the latter and of their outlines when viewed as in plate 

 III, figs. 1 and 3, or as in plate II, fig. 4, should give enough 

 detail for determination. 



Resting in part on the first epineurals of interradius 4 

 (plate III, fig. 3), there is a large plate that, with one or two 

 others, was thrust over the specimen, after its death, from the 

 fourth interradius. This movement thrust the third epineural 

 of the lower row in this figure over against its fellow of the op- 

 posite row, caught it by one of its aborad edges and turned it 

 on its long axis through a little more than ninety degrees. It 

 was also the cause of slight displacement of four first epineurals 

 and perhaps also, through plates now lost by weathering, of 

 the displacement of the secondary jaw of the first interradius 

 and the removal of other epineurals in advance of the moving 

 mass. This large foreign plate possesses the same dimensions, 

 the same curve of the convex distal end, the two slightly concave 

 portions of the margin following this on either side and the 

 broader, thicker orad end of an interradial marginal of this 

 species. It was exposed to the effects of weathering before the 

 other plates in its vicinity and has apparently lost a portion of 



