REPOKT ON THE CRINOIDEA. 



265 



The following table shows the great amount of variation in the proportions of the 

 hasal tube in other individuals of Rhizocrinus rawsoni, together with its diameter as 

 compared with that of the stem-joints. 



Species. 



Rhizocrinus rawsoni. 



Rhizocrinus lofotensis. 



How 

 obtained. 



"Blake" 



Challenger. 



Capt. Cole, 

 "Investigator." 



"Porcupine." 



Sars. 



Deptli. 



fathoms. 

 175 



900 



300 



862 

 300 



Basal tube. 



Height. 



5-5 

 5-0 



3-5 



3-0 



2-0 



Width. 



2-50 

 2-00 



3-00 



1-75 

 1-50 



N.B. — Pourtal6s described his largest specimen of Rhizucrinus 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 slightly more robust 

 than in Perrier's specimens which have such an extraordinarily elongated calyx. Both are 

 smaller 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 Pourtales 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 LIII. 

 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 whicli 

 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 

 (PL LIII. fig. 7). The length of the calyx is almost the same in both sjaecimens, 

 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 LIII. fig. 7) they expand very slowly upwards to the level of the lowest 



(ZOOL. CHALL. EXr. — PAKT XiXU. 1884.) 



li 34 



