Agelacrinidae and Lepadocystinae 
465 
The ambulacra appear to consist of two series of plates, more or 
less alternating, which rest upon the theca. On plate 18, several 
of these ambulacral plates have dropped off, leaving slightly con- 
cave depressions. The lateral covering plates of the subvective 
grooves are well preserved at the proximal ends of several of the 
ambulacra, notably between deltoids 20 and 21, where these 
covering plates are seen to meet along the median line at an acute 
angle. Covering plates are seen also between deltoids 21 and 22 
and between 20 and 23. In order to make the structure of the 
tegmen agree with the theory of an early trimerous structure, 
among the Echinoderma, leading subsequently to a pseudo-pent- 
amerism, it is necessary, in the present species, to regard the left 
primary branch of the subvective system, between deltoids 21 and 
23, as much abbreviated, compared with the right primary branch, 
between deltoids 20 and 23. From these primary branches, two 
secondary branches originate on the right, and two on the left, by 
bifurcation. The anterior primary branch does not lie directly 
opposite the posterior deltoid, 23, but is directed slightly to the 
right. (See text Fig. 7 A on page 466 in this Bulletin.) The 
lateral covering plates are oblong in form and very minutely 
striated in a vertical direction. There is no differentiation of 
these plates at the center so as to form a district oral group. 
Stereom-folds in pectinirhombs 1-5, sixteen; in pectinirhomb 
12-18, twenty; in pectinirhomb 14-15, nineteen; in pectinirhomb 
10-15, sixteen; and in pectinirhomb 11-17, twelve. 
The anal area (Fig. 6A) presents details not seen in preceding- 
specimens. In contact with plate 8 are four small plates, of which 
the two extreme are in contact also with plates 7 and 14, respec- 
tively. Another plate of about the same size is in contact with the 
middle part of the anal outline of plate 7, and two additional 
plates are in contact with plate 14. All of the plates in contact 
with plate 13 are of smaller size than any of the other plates belong- 
ing to the outer circle in the anal area, especially toward the upper 
left hand side of this area, but the details here cannot be defi- 
nitely determined. From the left side of the moderate depression 
within this outer circle of plates, a pyramid of small triangular 
plates, meeting at the center, projects, but their number is not 
known definitely. Judging from other specimens, the anal area 
has not yet been accurately worked out, or else it varies more or 
less in structure in different specimens. 
