274 



FISHERY BULLETIN OF THE FISH AND WILDLIFE SERVICE 



22 



20 



a 



I 18 



•J. 



K 



< a 



P4 



55 5f S5 S6 51 58 59 60 61 



6Z 63 6i 65 66 67 68 



NUMBER OF ANAL KAYS 



^ 70 71 1Z 75 n 7S 76 77 



FiGTTBE 2. — Fre(iuency distribution by number of anal rays of tliree foninion east-coast species of I'driiliclillnis. Xumlier 



of sijecimeus : 117 dtntutus, 153 lethustiyma. 111 allnyutta. 



figure 2 sho^YS the essential specific divergence of 

 ulbigutta from those two closely related species. 



Because the fin ray counts overlap more or less, 

 while at the same time being of prime importance 

 in separating the species, it is essential to make an 

 accurate count when using this character. In this ' 

 study every fin was counted twice, once on either 

 side, as a check. Since the fin rays are many and 

 the labor of counting tedious, great care and 

 jjatience must be exercised to insure an accurate 

 count. In practice, some means may suggest them- 

 selves to check the counts on both sides of part 

 of the fin. For instance, most specimens have 

 places where the interradial membrane is con- 

 spicuously broken. The number of rays up to such 

 a point is jotted down and when the count is made 

 on the other side this number is checked. Again 

 the count may be made in groups of five or ten 

 rays, a dissecting needle being used to point off 

 the groups. By adopting some such means of 

 facilitating the count accuracy is possible. 



DORSAL RAYS 



Although in the three common eastern species 

 the number of dorsal rays intergrades to a con- 

 siderable extent (fig. 3), it is a useful character, 

 supplementing the two previous ones for distin- 

 guishing doubtful specimens. In the separation 

 of cariforruc'us from aestuarhtfi, the numbei' of 

 dorsal rays intergi-ades somewhat less than the 

 number of anal rays. The methods of counting 

 and recording the munber of dorsal rays were the 

 same as stated for the anal rays. 



CORRELATION IN THE NUMBERS OF ANAL RAYS 

 AND GILL RAKERS 



Figures 1 to '?> show that the inimber of gill 

 rakers and that of the anal rays constitute the two 

 most divergent characters. By plotting these two 

 counts, one against the other, in a correlation table 

 (fig. 4), a striking proof of the essential specific 

 divergence of the three common eastern species is 

 obtained. Figure 4 has been prepared from the 



