no. 1612. ABNORMAL ARM STRUCTURE IN CRINOIDS—CLARK. 267 
united by syzygy, bears it on the same side, as is always the case when 
the second and third and third and fourth brachials are united by 
muscular articulation. But the third brachial is peculiar in bearing 
a pinnule on the same side as those of the second and fourth instead 
of on the opposite side. 
Heliometra tanneri (Hartlaub). (Fig. 4.) <A specimen of this 
species in the collection of the University of California, for the privi- 
lege of examining which I am indebted to the kmdness of Prof. W. E. 
Ritter, is peculiar in having an additional first and second brachial 
on one arm, inserted between the costal axillary and the normal first 
and second brachial. This interpolated pair of 
brachials is, in reality, @ distichal series, but with the 
more distal of the pair not an axillary; following the 
costal axillary, the joints may be described as follows: 
First, a first brachial, apparently in every way nor- 
mal; then a second brachial, but of the type belonging 
to the opposite arm of the pair, and therefore bearing 
the pinnule énteriorly instead of exteriorly, follow- | 
ing this is a normal first brachial, succeeded by a 
normal second brachial, and the succeeding brachials Fie. 4. —Heriome- 
as usual. This is interesting in being the only casein on Ne 
the thousands of specimens of species of this genus 9 witH THe First 
which I have examined in which a distichal serieswas fe 
present; and in this case it does not result in an extre 
urm, as the joint, which 1s in reality the distichal axillary, bears a pin- 
nule instead of the normal arm. It strongly suggests that the power 
of producing a distichal series and additional arms, latent in many 
ten-armed species of different genera, and in the case of Antedon 
bifida even in genera belonging to the same family, is quite absent 
in Heliometra. 
Hehhomeira maxima (A. H. Clark). (Hig. 5.) In a previous 
paper I restricted the family Antedonide, making it equivalent to 
the “ Tenella” and “ Eschrichti” groups of Dr. P. H. Carpenter, 
and the genus Promachocrinus as redefined by Minckert—that 1s, 
including only the species kerguelensis and vanhoffenianus. This 
was done on the basis of arm and pinnule structure and the structure 
of the distal radial faces. I placed Promachocrinus (restricted) 
next to Meliometra, believing it to be merely a meristic variation 
from that type, in the same way that Decametrocrinus is a meristic 
variation from Pentametrocrinus. A specimen of Seliometra 
maxima, taken off the southern part of Sakalin Island, appears to 
corroborate my views as to the origin of Promachocrinus from 
Heliometra, or some very similar form. This specimen has twelve 
arms, arising from six costal axillaries, which in turn rest upon six 
