GO 



BULLETIN: MUSEUM OF COMPARATIVE ZOOLOGY. 



there are now five accessory rays between 4 and 5, and four in each 

 of the interradii 1—2 and 3-4. The specimen of canopus with 20 rays 

 differs only in that there are three rays in interradius 2-3, and only 

 four in 4-5. An example of kubiniji with 21 rays gives the condition 

 shown in figure 4 (Plate 8), but specimens of canopus with 21 rays are 

 quite unlike this; one has six rays in 1-2, three in 2-3, four in 3-4, 

 three in 4-5, and none in 5-1, and the other has four, three, five, four, 

 and none, in the same order. Very similar to the latter is another 



canopus with 22 rays 

 arranged 4, 4, 5, 4, 0. 

 Specimens of kubiniji 

 with 23 and 25 rays 

 show the sequence 

 given in figures 5 and 

 6 (Plate 8). The 

 order 5, 5, 5, 3, 0, 

 seems to be the nor- 

 mal arrangement for 

 specimens of kulriniji 

 with 23 rays, but in a 

 specimen of canopus, 

 the order is 5, 3, 5, 

 5, 0. With 24 rays 

 the order in kubiniji is 

 5, 5, 5, 4, 0, while in 

 an example of canopus 

 it is 5, 3, 5, C, 0. With 25 rays, canopus and pohjbrachius both agree 

 with kubiniji in the symmetrical 5, 5, 5, 5, 0, and as this was found to 

 be true of all of the six Heliasters having 25 rays, which were examined, 

 it is fair to consider it the normal arrangement. In examples of canopus 

 and kubiniji with 26 rays each, the additional ray occurs in interradius 

 1-2. In examples of the same species having 27 rays interesting con- 

 ditions, undoubtedly abnormal, were found; in canopus (Plate 8, fig. 7) 

 there are two rays in interradius 5-1, the only case, among 30 Heliasters 

 examined, in which there are accessory rays in that interradius ; in 

 kubiniji, the stomach-muscle of 1 is missing, so that there are only four 

 such muscles and the sequence of the rays is 9, 4, 6, 3, 0, with, of course, 

 possible errors in the 9 and 0. After the number of rays gets beyond 

 26, there appears to be no uniformity in the order or position of the 

 accessory rays, as is clearly shown by the following table : — 



If &0 3.1 $2. 33 3* 35 2(o 37 32 39 ¥0 4/ 



Diagram 4. 



To show the relative abundance per thousand, of 77. heli- 

 anthus with 30-40 ravs. Based on 50 individuals. 



