163 
ing, especially because the coloration of the test is so very alike. 
In the tuberculation there is certainly no very great difference, 
though especially the primary interambulacral tubercles on the oral 
side are more distinctly confluent (and not separated by miliary 
tubercles) in albocinctus than is the case in magellanicus. But 
then the apical system affords striking differences, the genital and 
ocular plates of magellanicus being covered by numerous tubercles, 
while in albocinctus they carry only one single larger tubercle and 
some few miliaries. Oc. I is insert in magellanicus, exsert in albo¬ 
cinctus ; the anal plate is naked in magellanicus, while in albocinc¬ 
tus it carries one prominent tubercle. Also the size of the apical 
system and the periproct is different, being distinctly smaller in 
albocinctus as seen from the measurements of albocinctus given here, 
compared with those of magellanicus given in my Report on the 
Echinoidea of the Swedish South Polar Exped. p. 37. Then the 
colour of the spines is strikinglv different and finally, in spite of 
the doubt expressed by Clark as to the constancy of the char- 
acters of the pedicellariæ (without his having had the opportunity 
of studying them himself), the globiferous pedicellariæ are distinctly 
different, both in the structure of the valves and through the faet 
that in magellanicus there are two different kinds of these pedicel¬ 
lariæ, in albocinctus only one kind. 
There can thus not be the slightest doubt that albocinctus is 
quite disti.net from magellanicus. Whether it is also correct to place 
the two species in different genera, is not so certain. The only es- 
sential difference between the two genera, Notechinus and Pseud- 
echinus, is, in faet, that of the globiferous pedicellariæ. Since I have 
now found, on the rich material now at my disposal, that the oc- 
currence of a tooth on both sides of the blade in albocinctus is 
by no means so very exceptional, 1 agree that the distinetion is 
not very sharp. However, I think it advisable to retain the two 
genera for the present, especially in view of the faet that we know 
now at least two distinet species of each of them, which are both 
in perfeet conformity, as regards the said characters of the pedicel¬ 
lariæ. The final proof of the validity of the two genera must be 
afforded by the study of their larvæ. If the larvæ prove to belong 
to the same main type I would hardly think the distinetion of the 
two genera maintainable. In that case Notechinus becomes a syno- 
n* 
