290 THE VOYAGE OF H.M.S. CHALLENGER. 



eschrichti, there are few recent Comatulse with a calyx which at all approaches that of 

 many fossil species in size. 



The centro-dorsal of the' large Vienna specimen has lost all trace of its cirrus-sockets 

 on one side, and is almost reduced to a level with the radials ; while iu an "Alert" 

 specimen from Port Molle the sockets are all obliterated, leaving nothing but a thin flat 

 plate, very much as in some forms of Actinometra paucicirra (PI. LIV. figs. 1-4). The 

 calyx of the form from Cape York, which I have hitherto called Actinometra strota, is 

 represented in figs. 4, a-c, on PI. V. Except for the almost entire absence of a basal 

 star (fig. 4c), it is not greatly different from that of the individual from Singapore which 

 I figured in 1879 ; x but it is very much smaller than the calyx of Actinometra robusta, 

 which reaches 7 mm. in diameter, while 5 mm. is the maximum size of the Challenger 

 specimens ; and none of them show any trace of the curious diverticulum of the axial 

 canal into the substance of the radial which occurs in that variety. 2 



The large " Alert " specimen from Port Molle is also remarkable for having the disk 

 perfectly soft and membranous ; while in others from Port Curtis and Torres Strait it 

 is covered with minute polygonal plates, and the ambulacra are also strongly plated 

 as shown in Part I., pi. liv. figs. 10, 11. The ambulacral plating ceases entirely, 

 however, where the arms come off at the margin of the disk, and they have nothing at 

 all like the ambulacral skeleton which is often so fully developed in Antcdon and in the 

 Pentacrinidse. 



A large number of this species were obtained by the Challenger at Booby Island, 

 including several in a more or less immature condition. One of the smallest of these is 

 represented on PL LIII. fig. 1, and is noteworthy for the great relative length of its 

 arm-joints, as compared with those of the adult (fig. 2). 



Bell has given the varietal name albonotata to a specimen from Albany Island with 

 twenty to twenty-five cirri and but slightly keeled basal joints on the lower pinnules, in 

 which the coloration consists of white spots on a dark ground. 3 But the colour variations 

 of this species, even in one and the same locality, are almost as numerous as those of 

 Antedon carinata; and I cannot see much use in giving varietal names even to 

 forms which may seem to reach "the extreme limit of the species." Differences of colour 

 are in fact quite useless for the purpose of specific discrimination among the Comatulse. 



2. The Paucicirra-gvowp. 



Bidistichate species, with twenty arms or more ; the two outer radials and the first 

 two joints after each axillary respectively united by syzygy. 



Remarks. — This group includes only two species, which are closely allied to the 



1 Trans. Linn. Soc. Lond. (Zool.), ser. 2, 1879, vol. ii. pi. v. figs. 1-4. 



2 Ibid., p. 86. 3 "Alert" Report, p. 1C5. 



