294 DISCOVERY REPORTS 



Fig. H 

 All figures enlarged x 20, except 7 and 8 which are x 10 



1. Odinella mitrix Actinostomial ring viewed from outside, showing an interradius and the distal face of 

 second ambulacral and of first adambulacral plates where 2 rays have been detached, a^, first ambulacral 

 plates (dorsal surface); a", distal face of second ambulacral plates; ad^, distal, articulating face of first adam- 

 bulacral plates; /, interradial plate (odontophore) ; m, first pair of inferomarginal plates, closely apposed, 

 above the first adambulacrals; />', /)-, position of first and second ambulacral pores. 



2. Brisingella pusilla Fisher (California). Mouth-plate (s, x, y) for comparison with fig. 3. The plate is seen 

 from the furrow face, the actinal surface being in profile below. On the left the odontophore (z), marginal (m), 

 and first adambulacral {ad'^) are shown. In this genus the interradial angle (on the opposite side of ad^ and m) 

 is defined by these plates (fig. 8) ; v, groove of circumoral water tube at point where the radial tube passes to 

 right in groove r ; s, spine-bearing margin of plate ; in the groove above is the circumoral nerve ; x, lateral wing 

 of plate shown in figs. 7 and 8 viewed endwise ; y, shorter ventrolateral wing shown in fig. 7 ; z, dorsal wing 



(fig- 8). 



3. Odinella niitrix. Mouth-plate viewed from furrow face with interradial plate («) in position, a", articulat- 

 ing surfaces of first ambulacral plate; ad", same of first adambulacral; />', side of first ambulacral pore; r, 

 groove for radial water tube; i, spine-bearing margin of plate, the deep groove above for circumoral nerve; 

 w, groove for circumoral water tube; x, lateral wing of plate which joins that of neighbouring plate across 

 ambulacral furrow ; y, portion of plate which forms a ventrolateral wing in fig. 7 ; z, the dorsal extension of 

 plate (figs. 4, 6). 



4. Odinella mitrix. Segment of actinostomial ring viewed from the inner or oral face. On the right a pair of 

 mouth-plates, o, is hatched to differentiate them from the first ambulacrals (a^), one of which has been lifted 

 out. Note X, the lateral wing of each mouth-plate for comparison with figs. 5 and 7, and crossing it, v, the 

 groove of circumoral water canal ; 0' indicates position of muscles so indicated in fig. 6 ; z, the dorsal extension 

 of plate which locks with the first ambulacral. 



5. Odinella nutrix. A pair of mouth-plates seen from below. On either side is the first ambulacral plate a', 

 the left one is hatched; ad", the facet of plate with which the first adambulacral forms a muscular joint; 

 s, spine-bearing margin ; v, position of circumoral water tube ; x, lateral wing which joins that of opposite 

 side of furrow {x-x, fig. 4) ; y, portion of plate corresponding to y, fig. 7. 



6. Odinella nutrix. Segment of actinostomial ring viewed directly from above. On right, a single first 

 ambulacral plate is hatched. Note the broad muscular symphyses at o , o" directly below odontophore, i, in 

 contrast to the same in Brisingella (fig. 8). These confer a high degree of flexibility to actinostomial ring. The 

 first adambulacrals are shown in solid black beneath the second ambulacrals. The entire length of the first 

 inferomarginals, m, is shown, whereas in fig. i they are greatly foreshortened; z is the dorsal extension of 

 mouth-plate which forms a non-muscular symphysis with the first ambulacral. 



7. Brisingella pusilla. The ventral aspect of a segment of the actinostomial ring ( x 10) for comparison with 

 fig. 5. A pair of mouth-plates is dotted. The lateral extensions x-x (so marked in other figures) are notable for 

 unusual length. Above them passes the radial water tube, r; the ventrolateral wings, Y, are not present in 

 Odinella. One first ambulacral is hatched. Other letters: a^, a^ first and second ambulacrals; ad, first 

 adambulacrals ; m, pair of first inferomarginals defining the interradial angle ; /)>, p-, pores of first and second 

 tube-feet. 



8. Brisingella pusilla. Dorsal aspect of segment of actinostomial ring for comparison with fig. 6. On right 

 the odontophore, i, has been removed and a pair of mouth-plates dotted ; behind them as much as can be seen 

 of first adambulacrals, ad' is hatched. The lateral, x, and dorsal, z, wings of the mouth-plates o are con- 

 spicuous. Other letters as in fig. 7. 



9. Odinella nutrix. Ventral aspect of the interradial plate or odontophore. 



