1892.] PROF. F. J. BELL ON PONTASTER TENUISPINIS. 431 



says of a variety that its " habit " is much larger than that of " any 

 examples which I have seen of the type-form." The largest of his 

 varieties appear to have R=66, but Koreu and Danielssen had 

 examples of P. tenuispinis in which R:=130. However, it is 

 useless for anyone who has not, like myself, access to the collection 

 which Mr. Sladen describes, to hope to discuss with him any 

 question which is based on measurements, for of these no writer is 

 so chary. 



The proportions of R to r in this variety of Mr. Sladen's vary 

 from 3/jr, through 3|| and 4 to 4-^^^ and 4^ ; as the variability is so 

 great, T consider the relation of R to r should be put aside as a 

 reason for distinguishing a variety of a form which itself shows a 

 variation between 4 and 7f. 



The original diagnosis of the species begins with tlie words " radiis 

 attenuatis"; but in this point I observe some differences among the 

 specimens, some of which have arms a good deal stouter than others. 

 But on this point it is necessary to be precise, for Mr. Sladen's 

 variety, which he calls " platynota"^ (a misprint, I presume, for 



A B 



Diagram showing the relative proportions of tlie arms of (A) P, tenimpiim 

 and (B) P. platynotos. 



platynotos), is said to be marked by a " rapid attenuation " of the 

 rays at a short distance above their base. If figures can be made 

 to prove anything, words may be taken to mean anything ; and a 

 " rapid attenuation " may mean anything between the loss of weight 

 which follows a few days' hard exercise or the result of a ten-weeks' 

 bout of fever. When we bring this vague expression to the test of 

 measurement, we find that one example of the variety has an arm 



1 Ohall. Eep. Asteroidea (1889), p. 29. 



30* 



