1913] The Ottawa Naturalist. 79 



Adambulacrals. 



VI. The exposed flat faces of the first adambulacis 

 (mouth plates) dip strongly inward. The true oral surfaces 

 of these plates in Palaeaster parviusculus have similar flat 

 faces which also dip inward. See stereogram in [C] plate III. 



VII. Prof. Fisher says of the angular ridge towards the 

 furrow, which is shown by all the adambulacrals, "This strongly 

 suggests the attachment area of the 'furrow comb' of spines 

 * * * * such a ridge is quite characteristic of many species. It is 

 well seen in Astropecten, Psilaster, Persephonaster, etc." 



VIII. Dr. Ravmond says of these adambulacrals [B] p. 105, 

 lines 9-11, "And each plate was provided with a cup-like pit 

 into which the proximal end of a covering plate fitted." He then 

 says of the Urasterella which he figures, [B] 106, lines 1-2; plate 

 VI, fig. 1; that its apparent "Covering pieces" (ambulacra) 

 "are supported by small plates with a pit on top, just as in 

 Protopalaeaster narrawayi." Now, in the first place, ambulacra 

 never have their adambulacral ends fitting into cup-like pits to 

 form ball and socket joints. There is, however, a pit or depres- 

 sion between each pair of plates, and this is occupied by the 

 ambulacro-adambulacral muscle. In the second place, the 

 adambulacra now in question do not possess "cup-like pits," but 

 thev show angular, flat or slightly depressed muscle fields. In 

 the" third place, the proximal ends of the epineurals in 

 P. narrawayi not only do not "fit" these muscle fields, but 

 thev are in every case placed alternatelywith them. This is the only 

 evidence that Dr. Raymond deduces from the adambulacrals, and 

 it is too widely at variance with the facts to have been carefully 

 considered, the alternate arrangement just specified is strong 

 evidence against Dr. Raymond's interpretation. 



On giving these adambulacrals additional study by means of 

 new stereograms, I am inclined to abandon my idea that the 

 muscle fields in question were for attachment of epineural 

 adductors. The muscle fibers, which remain attached to them, 

 are small and more probably served to open the "furrow combs." 

 In our plate IX, fig. 2, much heavier bundles of muscle fibers are 

 to be seen next the marginals and between adambulacra note 

 particularly the remains of the bundle between the last two 

 adambulacra on the left. In addition to the evidence given, 

 [A] p. 46, lines 32-3 7, to show that the epineurals were arranged 

 alternately with the adambulacra, I here present fig. 1 of plate 

 IX. There maining ends of several epineurals are to be seen in 

 place in the left-hand row of this figure, but probably crushed 

 in a little by the force that displaced the epineural below. In 

 figure 2 of this plate it will be. seen that the median bosses 



