288 ./ K. Thacher — Median a7id Paired Fins. 



First Dorsal of Eulamia Milherti, PI. LII and LIU, figs. 28 and 24. 



Number of rays 28 or 29. ^ 



As indicated by the numbering of the rays, I take number 21 in each figure to be a 

 single ray, which has widened at the top, and been segmented in the way figured. 



Extra segmentations in fig. 23. rays 20 and 21 (2 extra segmentations in the latter) 

 in fig. 24, rays 4 and 21. This gives •!. 



Concrescence is estimated at -09. Betipping is absent. 



Ratio of proximal to middle piece •9. 



Ratio of distal to middle piece '9. 



Second Dorsal of Ealamia Milherti, PI. LIU. figs. 25 and 26. 



The number of rays differs remarkably in the two specimens, being 12 in the one 

 and 16 in the other. It must, however, be remembered that the second dorsal has 

 become very small and of very little physiological importance. Organs which have 

 thus become functionless are peculiarly prone to vary. They thus secure more easily 

 some other and new function. We will take the average number 14 as the normal one 

 for the rays of this fin. 



Extra segmentation occurs in fig. 25, ray 6 (twice), and in fig. 26, ray 3 This 

 gives •!. 



Concrescence is estimated at -09. 



Betipping is absent. 



Ratio of proximal to middle piece of middle ray -8. 



Ratio of distal to middle piece of middle ray -5. 



Anal of Etdamia Milherti, PL LIII, figs. 27 and 28. 



Number of rays 17 or 18. 



Extra segmentations in fig. 27, rays 7, 10 and 12 (twice in the latter); in fig. 28, 

 twice in 12, once in 16, give 2. 



This implies a certain interpretation of the ambiguous rays 11 and 12 in figure 27. 

 In fig. 28 we seem to have a plain case. Here the ray 1 2 is broadened at the top, and 

 its distal piece divided by two intersecting cuts into four pieces. Ray 12 in fig. 27 is 

 explained in the same way. Ray 11 is a little shortened, and excluded from the edge 

 by the tips of 10 and of 12. This appears to me the most probable view of the case. 



Concrescence is estimated at ■12. Betipping absent. 



Ratio of proximal to middle piece of middle ray -7. 



Ratio of distal to middle piece of middle ray -4. 



First Dorsal of Sphyrna zygcena, PI. LIII and LIV. figs. 29 and 30. 



Number of rays 33 and 34. 



I regard the three pieces at the extremity of 28 as belonging to that ray. It has 

 been widened and divided like the instances in Eula.mia. 



Extra segmentations, fig. 29, rays 2 and 3, twice; rays 4 and 5; ray 28, twice; fig. 

 30, ray 28, twice, give -2. 



Concrescence is estimated at -07. Betipping absent. 



Ratio of proximal piece of middle ray to middle piece 7. 



Ratio of distal to middle piece of middle ray 2-4. 



In fig. 29 the proximal line of segmentation fails in rays 9-17, except in the joined 

 rays U and 12 where it is present. In fig. 30 it fails in rays 8-16. 



