Dr. F. A. Bather on Protoechinus, Austin. 43 



two plates. Of these the one to the right, over which the 

 dotted line 5 passes, is turned up at the edge next the spec- 

 tator, but it must be a part of the second plate in column 5. 

 The small portion underlying it to the left may be a part of 

 the same plate in its normal position, or it might possibly 

 belong to the initial plate of column 6. The outwardly 

 splaying curves of the ambulacra just here render the 

 existence of a sixth column almost inevitable. 



Of these columns of interambulacrals, No. 1 is the least 

 disturbed. It consists of five plates, all, except the prim- 

 ordial, higher than wide and relatively thin ; the third plate 

 measures 8*2 mm. X4*5 mm., so far as visible. Towards the 

 peristomial margin the plates of this and of column 2 in- 

 crease in thickness, and the primordial plate itself is fairly 

 stout. The adradial edges of this plate, instead of being 

 merely bevelled off, are marked on each side with two curved 

 notches to receive the ambulacrals; and this confers greater 

 rigidity on the peristomial frame. The edges of the adoral 

 pair of notches are raised. The adoral margin of the plate 

 seems incomplete, and adoral to it a fragment of some plate 

 is seen in the matrix. 



The plates of column 2 as represented in the drawing do 

 not seem to tally with the corresponding plates of column 1. 

 It is, however, difficult to see the suture between the second 

 and third plates, and these may really be but a single plate. 



The plate at the beginning of column 3 displays part of 

 the outer surface, and this is covered with small secondary 

 tubercles. A primary tubercle, if borne by the plate, is not 

 seen on this exposed part. 



The initial plate of column 5 bears a circular depression 

 with central elevation, and this may be caused by the pres- 

 sure of a scrobiculate primary tubercle on its underlying 

 outer face. 



Of the Ambulacra, B is the better preserved. The notches 

 in the primordial interambulacral indicate that the first of 

 the coronal ambulacrals has been removed. Reckoning this, 

 we note in this column a five ambulacrals stretching to the 

 perradius and alternating with five of the adjoining column b. 

 Their width increases from 7'6 mm. to 8"9 mm. These are 

 succeeded by a row of four ambulacrals, and then, oddly 

 enough, the next row consists of only two very wide plates 

 {a being 9*2 mm. wide). After this the succession of four 

 columns reappears and, so far as can be seen, continues 

 regularly (a, a', b', b). 



In the right half of Ambulacrum D there was likewise a 

 scries of five plates before the column divided into two. Jn 



