Echinoid Tests, Diudcmoida. 
105 
already been noted by Duncan (1889, p. 80), precisely the same combination 
of primary ambulacrals is seen in Orthopsis itself, or at least in 0. miliaris 
and 0. granularis, the original species of that genus, though not in other 
species now referred to it. The diagnostic character that Gregory did empha- 
size was the single large main tubercle on the interambulacrals; but in 
maintaining that Hemipedina, no less than Diademopsis, possessed two small 
primary tubercles on each interambulacral, he must have forgotten «the entire 
absence of secondary tubercles from the areas» of H. Etheridgei, as described 
by Wright (Pal. Soc. Monogr. Ool. Echinoidea, p. 148). It is in fact this charac¬ 
ter that causes one to associate A. Thompsoni with Hemipedina rather than 
with Diademopsis or Orthopsis as those genera are usually understood. What- 
ever may be the fate of this species in some future recasting of the Diademine 
Classification, I cannot. think that at present Dr. Gregory has established its 
Claim to be separated generically from Hemipedina. 
Palaeopedina Lambert (1900, p. 22) seems to rest on rather an insecure foundation. 
The genotype is Diaderna globulns Ag. (in Leymerie, 1838), and to the genus 
are also referred Diadema minimum Ag. and Diademopsis Pacomei Cott. 
All these are Hettangian. Hemipedina Bonei Wr., which Lambert suggests as 
a possible member of the genus, is Bajocian. The diagnosis agrees in the 
main with those given by Lambert for Hemipedina and Diademopsis, but the 
following are points of difference : —■ (1) «Test subhemispherical to subglobular» ; 
but Diademopsis is said to be sometimes subconical, and not all species of 
Hemipedina are strictly rotular, e. g. H. Waterhousei , described by Wrigiit 
as «inflated», and H. tuberculosa, which he calls «hemispherical». (2) «Gill- 
slits deep,» those of Hemipedina and Diademopsis being described as feeble. 
This is a matter of comparison, but I should never have described the slits 
as feeble in, say, H. perforata. (3) «Pore-pairs pseudo-bigeminate near the 
peristome.» All or nearly all Diademina have those pore-pairs in the stage that 
Lambert calls «pseudotrigemines», and, since this peculiarity is not alluded to 
again, I imagine that the latter was the word here intended. (4) «Main inter¬ 
ambulacral tubercles nearer to the adambulacral margin than to the median 
line, accompanied by less developed secondary rows which thin out above» ; 
this is precisely the same as in Lambert' s diagnosis of Diademopsis. (5) «Apical 
System either dicyclic, with periproct shifted posteriorly by a suranal, or hemioli- 
cyclic (some plates of the second circlet intercalated between those of the 
first).» This seems to be the real character on which the genus depends, 
since, in the paragraph following the diagnosis, the presence of a more or 
less persistent suranal is mentioned as the chief character separating Palaeo¬ 
pedina from Diademopsis and Hemipedina, and on p. 28 it is the only 
character so mentioned. 
First then let us consider the facts as to the occurrence of the suranal 
in Palaeopedina. On p. 25 the suranal of P. globulus is said to exist «au 
moins chez les jeunes», a Statement implying that it is not always found in the 
adult. On p. 26 the evidence is thus summarised: «Usually the position of 
the suranal is clearly indicated by angularity of the anterior border of the 
periproct; in some individuals however the suranal has been less developed, 
and is so to speak confounded with the anal plates in the irregularly circular 
