1912] Thb Ottawa Naturalist. 23 



its orad end by separation of weathered cleavage planes of the 

 ;alcite. In spite of the losses it has received it still appears to 

 be an interradial marginal of this species but belonging to another 

 specimen. 



A search for ambulacrals was made along the grooves left 

 between the adambulacrals in the older portion of the arms. 

 The weathering of the material rilling these grooves had left a 

 fine residual sand which could be easily removed. The groove 

 of arm I was excavated to considerable depth (compare figures 

 1 and 3 of plate I), but no trace of any plates lying between the 

 adambulacrals could be discovered. 



That the arms had no true stelleroid ambulacrals and also 

 no ossicles on their aboral surfaces is unmistakably suggested 

 by two cross sections of the arms shown in plate II. Figure 

 5 is of rav V at the aborad surfaces of the second arm marginals. 

 The rest of the arm had been here lost and the blackened cor- 

 bonized bed on which the arm rested could be easily removed. 

 The excavation w T as continued below the very definite line 

 between the blackened bed and the lighter colored limestone of 

 the matrix. After cutting down to a greater depth than that 

 of the marginals themselves a bit of cover glass w 7 as placed on 

 edge and allowed to rest against the faces of the marginals. 

 The transparent liquid gum was then gradually filled in back of 

 the glass and the photomicrograph taken from a position as 

 near the horizontal as the specimen could be placed before the 

 objective of the microscope. The blackened porous bed is 

 seen to be attached to the outer edge of the marginals and 

 to strike diagonally across the interradial spaces both to the 

 right and to the left (interraclii 4 and 5). No trace of any 

 aboral plates is here revealed and ambulacrals are alscfwanting. 



Figure 7 of plate II represents a cross section of arm III 

 at the aborad surfaces of the sixth pair of arm marginals. The 

 cut here under the lost portion of the arm was made to a still 

 greater depth but sloping away from the arm plates in order to 

 avoid accidental loss as these plates are very delicately attached 

 to the bed. The low r er edge of the circular covering glass is 

 here seen and show's the depth of the excavation. The adam- 

 bulacrals are almost in contact with each other. Again there is 

 neither trace of ambulacrals or of aboral plates. The blackened 

 porous bed is however still present. 



In plate III, fig. 5, what is apparently the broken edge of 

 the remains of a thick leathery integument is seen to run from 

 arm IV across the interradius to arm III. Figure 3 of plate I 

 shows that the remains of this integument blackened all the 

 interradial spaces and followed the more distal borders of each 



