REPORT ON THE CRINOIDEA. 
265 
The following table shows the great amount of variation in the proportions of the 
basal tube in other individuals of Rhizocrinus rawsoni, together with its diameter as 
compared with that of the stem-joints. 
How 
Species. obtained. 
Depth. 
Basal tube. 
Length 
of Stem. 
fathoms. 
f “Blake” 175 
Challenger. 900 
Rhizocrinus rawsoni. \| Capt. Cole, 
| “Investigator.” 
“Porcupine.” | 862 
Rhizocrinus lofotensis, Sars. 300 
Height. | Width. 
55 2°50 
5:0 2-00 
3°5 3°00 
3:0 1-75 
2-0 1:50 
mm. 
Stem-joints, 
Number. | Length. | Width. 
68 
53 
45 
30 
67 
3°50 2°25 
300 2:00 
3°50 2°25 
2°25 1:25 
1°50 0°50 
N.B.—Pourtalés described his largest specimen of Rhizocrinus lofotensis as having a stem nearly 130 mm. 
long and composed of fifty-nine joints, the length of which averages three times their diameter. 
It will be seen from the above table that in absolute size, as well as in the proportions 
of the basals and of the stem-joints, the “ Porcupine” examples of this type are those 
which approach Rhizocrinus lofotensis most nearly ; though the stem is shghtly more robust 
than in Perrier’s specimens which have such an extraordinarily elongated calyx. Both are 
sinaller than those from the Azores, which are themselves smaller than the Caribbean 
specimens (though not always so in the length of the cup), a fact which is doubtless due 
to variations of temperature. The difference in size between the largest individuals of 
Rhizocrinus lofotensis found by Sars and Pourtalés respectively is likewise probably the 
result of the difference between the temperature of the Gulf Stream in the Florida Straits 
and that of the north-east Atlantic. 
The youngest specimens of Rhizocrinus rawsoni which I have seen are those dredged 
by the “Porcupine” in 1869 at a depth of 1207 fathoms off Cape Clear (Pl. LIIL. 
figs. 7, 8). Each has twenty-eight joints in the stem from the calyx to the root; but 
its length, which is only 20 mm. in the smaller, is 24-5 mm. in the larger individual. 
The uppermost joints are decidedly wider than those below them, the majority of which 
are elongated and cylindrical, only a few at the base of the stem (more in the larger than 
in the smaller individual) having the characteristic dicebox shape, with expanded ends 
(PI. LIU. fig. 7). The length of the calyx is almost the same in both specimens, 
1°8 mm., though its diameter across the radials is greater in that which has the longer 
stem.~ It is mainly formed by the basals, which are 1:2 mm. in height. In the smaller 
individual (Pl. LIM. fig. 7) they expand very slowly upwards to the level of the lowest 
(Z00L. CHALL, EXP.—PART XXxl,—1884,) 
Ti 34 
