78 .The Ottawa Naturalist. [Oct. 



III. The absence of granular ornamentation on the 

 exposed faces of the arm marginals is about equal in transverse 

 width to the area which would be covered with the opened 

 epineurals. Dr. Raymond, [B] p. 106, lines 42-43, cites this 

 peculiarity as evidence that supero -marginals must have rested 

 over these. In [C] I have published stereograms of three different 

 regions from the undoubted oral surface of Palaeaster niagarensis, 

 Hall, which show the same smooth surfaces, and Prof. Fisher 

 writes me that naked areas on these plates "are especially 

 numerous in the Goniasteridae, in the genera Tosia, Goniaster, 

 Pseudarchaster, Plinthaster." The evidence here is at least no 

 stronger for an aboral than an oral surface. 



IV. Dr. Raymond, [B] p. 106, lines 38 and 42, calls the 

 exposed surface of the marginals "truncated" and "flat." We 

 have seen that this is far from being the condition of the inter- 

 radials and in [A] plate II, figures 3 and 4, we may see that it 

 does not accurately describe the arm marginals. The first of 

 these has a fairly well rounded surface, while the second to the 

 fifth possess well marked angles a little orad of the centre of the 

 plates. That these plates were convex on transverse vertical 

 section is also seen in figures 5 and 7 of this plate note particular- 

 ly the right-hand side of figure 7. 



Photomicrographs made under gum possess a flat lighting 

 that is sometimes very deceptive. My study of such, like the 

 one used in figure 2 of the plate just referred to, led me also to 

 call these plates flat and deny them re-entrant angles for the 

 oral longitudinal muscles. If now we will examine in [A] plate 



III, fig. 4, the marginals numbered from 2 to 7, we shall see 

 these plates in normal lighting and their appearance is very 

 decidedly that of original free surfaces and against both Dr. 

 Raymond's descriptive terms and his deduction therefrom that 

 these surfaces were produced by intimate contact with a series 

 of supero-marginals. Many forms, both living and fossil, show 

 a more decided oral flattening of these plates than that revealed 

 in this figure. 



V. In our present plate IX, fig. 1 , the right hand marginals 

 5 and 6 are fairly well preserved and the fields of their common 

 flexor clearly outlined both by form and also bv the blackened 

 remains of some of their muscle fibers. Such large bundles of 

 flexors would occur only on arm surfaces. 



Of the five items given by the marginals the third is of little 

 value and is only included because it formed a part of Dr. 

 Raymond's evidence against an "oral side up" decision. Item 



IV, when the real facts are given, is for such a decision, and 

 items I, II and V are of a most positive and unequivocal 

 character. 



