920 
MR. P. H. CARPENTER ON A NEW 
The total width of the calyx across the disc is barely 2 millims.; and the height of 
the centrodorsal and radials together is about the same. The former (Plate 71, 
figs. 1-4, cd) is rounded below, with its central canal completely closed up, so that it 
must have been detached for some little time from the remainder of the stem. The 
bases of half a dozen cirri are attached to it, and there are pits for the reception of 
two or three more. In the largest stump which is preserved (Plate 71, figs. 1, 3, c) 
the first two joints are quite short, as is usually the case, but the third reaches 
a length of 1 ’5 millim., so that the cirri must have been very like those of Eudio- 
crinus semperi. Except in this respect, however, and in the presence of five undivided 
arms, there is no further resemblance between the two types; for Eudiocrinus has a 
rosette, and consequently no basals appear externally. The radials are also only 
partially visible, owing to the extension of the centrodorsal over their lower surfaces, 
and the oral plates of the larva do not persist in the adult. But in Tliaumatocrinus 
(Plate 71, figs. 1-4) there are relatively large basals (b), which completely separate 
the centrodorsal (cd) from the radials (r). This is itself an unusual feature in anv 
Comatida, as will be explained further on. 
Upon these five basals there rests a ring of ten arched plates, five of which (r) bear 
the arms, and are evidently the radials. But they are not in contact laterally, as is the 
case in every other five-rayed Neocrinoid with which I am acquainted, for they alternate 
with five smaller plates (i, i), which rest upon the truncated apices of the basals, 
while the radials rest in the angles formed by the adjacent sides of every two 
contiguous basals. Four of these five interradial plates terminate in a free edge at 
the margin of the disc; but the fifth, that on the anal side, bears a small tapering 
appendage of four or five joints, the last of which seems to end freely (Plate 71, 
figs. 2, 4, 5, eta). 
The arms are composed of somewhat elongated joints, the second of which (Plate 71, 
figs. 1 , 2, 4, b. 2 ) bears the first pinnule. This is on the right side in three arms, and 
on the left in the other two. A similar variation occurs in Eudiocrinus semperi, but 
I do not attach much importance to it. The pinnules are very slender and delicate. 
The disc resembles that of Hyocrinus. Its central portion is occupied by a 
relatively large oral pyramid (Plate 71, fig. 5, o), while between this and the margin 
are two or three irregular rows of small anambulacral plates (Plate 71, figs. 1—5, an), 
some of them extending up on to the lower part of the long anal tube (at). The 
large size and comparatively dense appearance of these orals indicates that they are 
not undergoing the process of resorption as those of other Comatulce do. In some 
species (e.g., Ant. dentata, Say —A. sarsi, Dub. and Kor.) the process is completed long- 
before the end of the pentacrinoid stage; but in Ant. rosacea the orals persist in 
a partially resorbed condition after the loss of the stem, though they soon disappear 
completely. 
Thaumatocrinus is thus the only Comatida yet known in winch the oral plates 
of the larva persist, as they do in Hyocrinus and Rhizocrinus. The other peculiarities 
