263 
of the calyx, between which are deep clefts extending inward between the centrodorsal and the 
radials as in Zcnomctra and the large species of PsatJiyromctra. 
This genus includes only the following species. 
I. Atopocrimis sibogac A. H. Clark. 
A. H. Cl.ARK. Notes from the Leyden Museum, vol. 34, p. 151. 
Stat. 177. 2° 24.5 S., 129° 38.5 E. Ceram Sea. 1633 Metres, i Ex. 
The centrodorsal is elongate conical, 5.5 mm. broad at the base and 7 mm. long, the 
sides straight. Five strong interradial ridges each about as broad as the adjacent columns of 
cirrus sockets divide the lateral surface of the centrodorsal into five radial areas each of which 
is divided by a narrow median ridge which, except at the base, is as high as the interradial 
ridges. The distal border of each cirrus socket is produced outward forming a strone rid<ye 
across the proximal border of the one next below. Thus each cirrus socket occupies an 
approximately oblong rather deep pit bounded proximally and distally 
by these ridges just described, and laterally by the longitudinal interradial 
and radial ridges. There are thirteen or iourteen cirrus sockets in each 
radial area, making about sixty-eight in all. The youngest cirrus sockets, 
on the proximal margin of the centrodorsal, project above the general 
surface of the latter, appearing like the first segment of a cirrus. Each 
cirrus socket bears on either side of the minute central canal (which is 
slightly below its centre) a strong rounded (^fulcral) ridge; this, like the 
produced distal border of the cirrus sockets, gradually decreases in 
height proximally, but much more rapidly decreases in height distally. 
These transverse fulcral ridges are on either side produced outward to ^'s- '5- 
. . . Lateral view of the specimen 
a pomt which is somewhat higher than the general surface of the inter- d Atopocrinus sibo^ae Uaxa^xsx. 
radial and the radial ridges between the columns of cirrus sockets, so i77- X 2- (Courtesy of the U.S. 
'^ National Museum). 
that in j)rofile these ridges appear very strongly serrate, the radial rather 
more so than the interradial, the teeth of the serrations being convex proximally and concave 
distally; in a lateral view of the centrodorsal these projections appear as alternating bracket-like 
processes proximally arising gradually but distally terminating abruptly in a straight horizontal 
border. On the interradial ridges these projections are separated by a median free bare area 
about equal to their own lateral height, but on the radial ridges they occur almost in a straight 
line. As in Zenometra and in Psathyrometra deep subradial clefts occur between the radials 
and the centrodorsal; in height these are equal to one half of the dorsoventral diameter of the 
topmost fully developed cirrus sockets. 
High and narrow basal rays, of which the outer ends are broadly pentagonal and 
convex, cap the proximal ends of the interradial ridges and e.xtend inward under the radial 
pentagon, forming the sides and the blind inner wall of the subradial clefts. 
The cirri are lacking. 
The radials are about twice as broad as high in the median line, but recumbent, so 
