2 66 
the triangular form not becoming pronounced until after the third or fourth ; and (6) the second 
segment of the lowest pinnules is very short. Clearly, therefore, Atopocrimts cannot belong to 
the Pentametrocrinidae. 
Atopocrinus suggests the genus Zenometra in certain ways — the arms are stout and 
robust, and the conical centrodorsal is divided into ten sharply delimited areas each with a 
column of cirrus sockets, but (i) in Zcnonictra the disk is broader and the ambulacra run 
direct from its surface to the ventral surface of the arms; (2) the earlier brachials and the first 
syzygial pair are oblong; and (3) the cirrus sockets have no fulcral ridges. 
In (i) the details of the arrangement of the cirri on the centrodorsal, in (2) the details 
of the structure of the cirrus sockets, in (3) the structure of the disk, in (4) the triangular 
brachials at the base of the arms, and especially in (5) the triangular first syzygial pair, 
Atopocrimis agrees with AtclecrimLS and differs from all other comatulids. 
Atopocrimts differs from Atelecrituis (i) in having no basals, (2) in having only five 
arms, and (3) in having all of the pinnules present. 
Though very large in Atelecrimis afioniahts^ the external basals become very greatly 
reduced in such species as A. sitlcaius^ the variation in size being so great as to suggest 
that their presence or absence does not constitute a valid major character in the diagnosis 
of the family. 
In the family Zygometridae one of the genera, Etidiocrimis^ possesses only five arms, 
so that the same condition in a single genus of another family might be anticipated. 
In the Comasteridae, Colobometridae, Zenometrinae, Perometrinae and Pentametrocrinidae 
species (or genera) with deficient, and also with complete, pinnulation are found; it is therefore 
quite natural that there should be a genus of Atelecrinidae with complete pinnulation. 
Since the differences between Afopocrimis and Atelecrimis are of relatively small impor- 
tance while the differences between Atopocrinus and all the other comatulid genera are 
fundamental, we appear to be abundantly justified in placing Atopocrimis in the Atelecrinidae. 
Atelecrinus P. H. Carpenter. 
Key to the Species of the Genus Atelecrinus. 
a^ The centrodorsal bears 15 columns cirrus sockets (Hawaiian Islands). . conifer 
a- The centrodorsal bears 10 columns of cirrus sockets 
b^ basals very large, the height equal to more than half the width ; no raised 
rim about the cirrus sockets; cirri with 19 — 20 segments, of which the 
outer are but little longer than broad, ending in a stout recurved claw 
(Moluccas). anoinalus 
\y basals very low, forming a narrow band between the radials and the centro- 
dorsal, or reduced to low triangular areas in the angles of the calyx ; a 
horseshoe-shaped rim borders the cirrus sockets proximally and laterally 
c^ on the surface of the centrodorsal the columns of cirrus sockets are 
segregated in five pairs by relatively broad shallow interradial grooves; 
