272 ^Ir. F. A. Bather on PlioliJocidaris anceps. 



avoid — a mistake due to the fact that the specimen is seen 

 from the inside. In numbering the columns of inter- 

 nmbuhicrals I forgot to reverse my tracing, as 1 had intended, 

 with the result that the ininibers on the dia;,M-am (p. 48) are 

 wrong. This was poiutt^d out by my friend Dr. R. T. Jack- 

 son in a letter of l4th Feb., 1918. As the simplest way of 

 ])uttingthe matter right, I avail myself of his kind permission 

 to print some of his informal remarks, and reproduce the 

 diagram with corrected columns and numbers. 



Protoechinus 



ANCEPS AuatlO 



HOLOTYPK 



X *)/ '•.-.sm. 



Dr. Jackson writes : — 



" As regards the numbering of columns in interambulacrum 

 0, as it is an internal view I should have column 1 on 

 the right (compare Penschodomus, my plate 6-4, fig. 2). 

 Column 2 would then come on the left, column 3 would fall 

 to the right, with the second ])late truncating its dorsal 

 border as usual. Column 4 would then start in a plate which 

 is practically pentagonal and on the right of the centre. This, 

 which I call the initial plate of column 4, does not make a 

 very good plate for the second plate in column 3, following 

 your lettering. Column 5 starts with a pentagon, and, as T 

 imagine, passes thiough the small fragmentary plate on the 

 dorsal border of the initial pentagon. The plate on the left 

 (if there are two plates, which looks probable to me) would 

 apparently then be the initial plate of column 6, which falls 

 to the left ot the centre (ri^,^ht of the centre as seen from the 

 outside). All this something as I show in IlyattecJunus 



