REPORT ON THE CRINOIDEA., 85 
It is concealed in the smaller specimen by the large and prominent anal tube which pro- 
jects forwards over it. The original of Hyponome sarsii, the “recent Cystidean,” was 
the disk of a plated Antedon, very probably of this species, Antedon multiradiata. 
Allusion has already been made to the frequency with which these disks are met with 
in an isolated condition ; and their resemblance to the curious Paleozoic forms Agela- 
crinus, Lepidodiscus, &e., is very striking. I know that Sir Wyville Thomson had a 
suspicion whether these problematical organisms may not have been the separated 
disks of some one or other of the numerous Palocrinoids, as suggested by Lovén and 
Liitken.* 
Deep ambulacral grooves with strongly plated sides are also met with on the disk of 
Actinometra strota. This species is very common at Cape York, and its disk, which was 
also obtained in an isolated condition, may be nearly bare, or plated very completely, as 
is shown in Pl. LIV. fig. 10, and Pl. LV. fig. 2. The whole of the large interpalmar area 
in which the anal tube is situated is covered with more or less scaly plates, which become 
stouter and more granular in the neighbourhood of the subcentral anal tube. The sides 
of the deep ambulacra are bounded by numerous smaller plates without any definite 
arrangement. But they are strictly limited to the disk, not extending on to the arms. 
The large size of this armature, relatively to the tentacles and the ambulacral groove proper, 
is well shown in the cross-section represented in Pl. LIV. fig. 11. Much of it extends 
beneath the water-vessels, and corresponds to what Miiller called the subambulacral 
plates of Pentacrinus’ (Pl. LXILI.). 
Actinometra jukesi is another species which is common at Cape York. The large anal 
area is often beset with numerous irregular plates, many of which bear nodules of variable 
size (Pl. LV. fig. 1). They are smaller on the base and sides of the anal tube; and 
there are few or none in the small interpalmar spaces between the edge of the disk and 
the circumferential ambulacra, which are themselves devoid of supporting plates, 
though deep like those of Actinometra strota. 
Some species, both of Antedon and Actinometra, have the ventral perisome of 
disk and arms entirely devoid of any continuous plating; though this may be strongly 
developed between the lower divisons of the rays, sometimes extending up to the level of 
the third axillary. 
C. Tue ViIscERAL SKELETON. 
I use the term “ visceral skeleton” to denote the numerous spicules and networks of 
limestone which occur more or less plentifully in the bands of connective tissue that 
traverse the visceral mass of the Comatule. It also includes the more or less regular 
plates, often quite well defined, which occur within the disk of Pentacrinus. They are 
1 Canad. Nat., 1869, p. 268. 2 Bau der Echinodermen, pp. 57, 58, Taf. vi. figs. 7, 9, d. 
