272 Mr. F. A. Bather on Pholidocidaris anceps. 
avoid—a mistake due to the fact that the specimen is seen 
from the inside. In numbering the columns of inter- 
ambulacrals I forgot to reverse my tracing, as I had intended, 
with the result that the numbers on the diagram (p. 48) are 
wrong. This was pointed out by my friend Dr. R. T. Jack- 
son in a letter of 14th Feb., 1918. As the simplest way of 
putting the matter right, [ avail myself of his kind permission 
to print some of his informal remarks, and reproduce the 
diagram with corrected columns and numbers. 
HioLerypz 
X %, diam. 
FPROTCECHINUS 
ANCEPS Austin 
Dr. Jackson writes :— 
“‘ As regards the numbering of columns in interambulacrum 
C, as it is an internal view I should have column 1 on 
the right (compare Perischodomus, my plate 64, fig. 2). 
Column 2 would then come on the left, column 3 would fall 
to the right, with the second plate truncating its dorsal 
border as usual. Column 4 would then start in a plate which 
is practically pentagonaland onthe right of thecentre. This, 
which J 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 I 
imagine, passes through 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 of the centre (right of the centre as seen from the 
outside). All this something as I show in Hyattechinus 
