220 
the foramen magnum, the Stirodonta have keeled teeth and narrow 
epiphyses, not meeting in suture over the foramen magnum, and 
the: Camarodonta have keeled teeth and wide epiphyses, meeting 
in suture over the foramen magnum (p. 183). The Au/odonta in- 
clude the families Heémicidaridæ, Aspidodiadematidæ, Diadematidæ 
and Echinothuridæ; the Stirodonta include the families Saleniidæ, 
Phymosomatidæ, Stomopneustidæ and Arbaciidæ; the Camarodonta 
include the families Temnopleuridæ, Echinidæ, «Strongylocentrotidæ” 
and Echinometridæ. 
With this classification (— excepting the position of the Echi- 
nothuridæ and, perhaps, the Stomopneustidæ —) I agree, of course 
— it is, in fact, very nearly the same classification which I have 
set forth in my ”Siam-Echinoidea” (p. 55—56), the difference being 
only (besides the Echinothuridæ) that I placed the Stomopneustidæ 
among the Camarodonta (my Tribus 4), while Jackson includes 
that family in the Stirodonta which contain both my tribus 2 (the 
Salenina) and tribus 3 (the Phymosomina). (Regarding the Salenina 
I stated (p. 55) that Fit is perhaps not unreasonable to see their 
nearest allies in the Arbaciidæ”). One of the main characters of 
my classification was the structure of the teeth: keeled or unkeeled, 
a feature which had not hitherto been taken into consideration. Ié 
is Jackson's merit to have noticed the other important features 
of the masticatory apparatus, of which especially the "fforamen 
magnum” appears to have an important bearing on the grouping 
of the Diadematoidea. Jackson does mot fail to notice that I. 
was the first to draw attention to the classificatory value of the 
structure of the teeth — he might also have noticed that the classi- 
fication of the Diadematoidea to which his researches have led bim 
is practically the same as that set forth by me (with the exceptions 
pointed out above). The fact that both of us have thus reached 
practically the same conclusions as to the mutual interrelations of 
all these forms is a sign that we are now well on the way to 
having their classification settled in accordance with their true 
natural relationship. 
