1885.] Progressive and Retrogressive. 241 
early in geological time, and as it is largely represented now in 
the abyssal ocean fauna, there is every reason to regard it asa 
degenerate type. The Scyphobranch line presents a specializa- 
un 
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tion of the superior pharyngeal bones, which is continued by the 
Haplodoci (Batrachidz). This cannot be called a degenerate 
line, although the fin-rays are soft. The Heterosomata (flounders) 
VoL. XIX.—=NO. III, 16 
