l8o NEW YORK STATE MUSEUM 



Devonic was signalized, in some cases at least, by the development of 

 anguilliform types, a very excellent illustration being furnished by one of 

 the three species of Mylostoma referred to on page 149 of this Memoir.' 

 We are confronted, too, in the modern fauna with a scant number of 

 Dipnoan and Crossopterygian survivors which exhibit the usual long- 

 bodied or eel-shaped contours of decrepit derelicts. 



It will be profitable for us to note some of the instructive examples 

 offered by Smith Woodward for illustrating the development of paired fins, 

 and also those that foreshadow adaptation to a terrestrial habitat. These 

 are among the most important conclusions that can be drawn from the 

 standpoint of comparative anatomy and phylogeny, and inasmuch as they 

 have a direct bearing upon our study of the local fauna, we may allow the 

 author to develop them for us in his own words. The following passage is 

 taken from the presidential address above referred to : 



Dawn of paired fins. No link is known between the Ostracoderms (or 

 Ostracophores) just described and the typical fishes which have a lower jaw 

 and paired fins ; and it is evident that the latter had already appeared in 

 Silurian times before they possessed a skeleton hard enough to be preserved 

 among fossils. The Silurian and earliest Devonian Acanthodians, however, 

 can not be far from the beginning of these typical fishes, and they seem to 

 show how paired fins began. 



These very old Acanthodians are known because they are completely 

 covered by small, hard skin granules like those of the oldest fossilized 

 Ostracoderms. Not only did the armour begin here in the same way as in 

 the Ostracoderms, but there was also an occasional fusion of the skin 

 granules into plates where stiffness was possible or necessary. A few rows 

 of the granules fused together at the front edge of the median fins above 

 and below the body, thus forming cut waters or " spines " ; and as a double 

 series of exactly similar " spines " occurs along the lower border of the 

 abdomen where the two pairs of fins are found in later fishes [cf. text fig. 1 7], 

 it is reasonable to infer that these are likewise the stiffened front edges of 

 fins. In other words, paired fins were not originally restricted to two pairs, 

 but formed a double series along the entire length of the abdomen. There- 

 fore, if the separate median fins were produced by the subdivision of a 

 primitively continuous median membrane along the back and the lower side 



' A new species, to be described under the name of Mylostoma newberryi in 

 a forthcoming number of the Bulletin of the Museum of Comparative Zoology, 50: 224. 



