J. K. Thacher — Median and Paired Fins. 289 



Second Dorsal of Sphyrna zygcena, PL LIV, tig. 31. 

 Number of rays 14. Extra segmentations amount to 10. 

 Concrescence is estimated at '07. 

 Betipping is absent. 



Ratio* of proximal to middle piece of middle ray -3. 

 Ratio of distal to middle piece of middle ray -3. 

 The last ray, both in the second dorsal and the anal, is large and round. 



Anal of Sphynia zygana, PI. LIV, fig. 32. 

 Number of rays, 27. 



Extra segmentations 8 (1), 9 (1), 10 (1), 11 (1), 12 (1), 13 (1), 14 (1), 15 (1), 16 (1), 

 17 (i), 18 (2), 19 (1), 20 (1). This gives "5. 



Concrescence is estimated at -03. Betipping none. 

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

 Ratio of distal to middle piece of middle ray -3. 



First Dorsal of Eugoynpliodus litoralis, PI. LIV, and LV, tigs. 33-39. 



Specimens figured in tigs. 33, 34 and 36 have plainly 16 rays. Those in figs. 37 

 and 39 have plainly 17. Those in tigs. 35 and 38 have 16 separate rays, but the last 

 is quite broad. Where we have plainly 17 rays, figs. 37 and 39, the last two rays 

 have united with the exception of their distal joints. We may fairly conclude that 

 figs. 35 and 36 present a more complete concrescence of those rays. We have then 

 as the number of rays 16 or 17, the former in three cases, the latter in four. 



Extra segmentation is estimated at '7. Concrescence is estimated to be "05. 



Betipping reaches -4, each separate piece being counted. These small nodules of 

 cartilage sometimes seem very evidently to be a continuation of a ray upon the fol- 

 lowing ray. But not infrequently they seem to be scattered rather irregularly along 

 the edge of the fin. It will be noticed that they are most frequent in the orad part 

 of the fin, though not on the first two or tliree rays. It is very probable that the 

 estimate of their frequency should be higher than given, for they are easily lost in 

 the preparation of the specimen. 



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

 of middle ray -4. 



Second Dorsal of Eugomphodus lltoralis, PI. LV and LVI, figs. 40-46. 



In fig 42 we have 16; in 45, 17 ; in 40 and 46 we have 18 rays. These are all plain 

 cases. Fig. 43 exhibits 17 rays, but raises a suspicion of 18 by the breadth of the 

 last ray. Pig. 41 gives 16 or 17, probably the latter. Fig. 44 leaves us in doubt 

 between 14, 15 and 16, with, as it seems to me 15, the most probable. We may take 

 17 as the normal number. As far as the evidence here goes the second dorsal is 

 more liable to vary than the first. We see that in each the greater the number of rays, 

 the greater is the amount of concrescence. 



Extra segmentation amounts to "6. 



Concrescence amounts to -10. Betipping amounts to -4. 



Ratio of proximal to middle piece of middle ray is '3. 



Ratio of distal to middle piece of middle ray is -3. 



* Where a segmentation is double the point half way between the joints is taken as 

 the limit between the middle and extreme piece. Where it is triple the middle seg- 

 mentation is taken. 



Trans. Coxn. Acad., Vol. III. 37 February, 1877. 



