922 The American Naturalist. { November, 
genus apiece for these creatures ample warrant for their con- 
clusions; but when we examine the actual significance of this 
difference in the number of holes in the side of the neck, most 
if not all the value of this character is destroyed, for the num- 
ber of functional gills is the same in both animals? The facts 
are that both animals have 5 gill-bars, but only 23 gills; that 
the first and second gill-clefts are in both forms devoid of a 
respiratory membrane or structures, although their secondary 
blood supply through the bronchial artery still persists. These 
two pair of gills are completely atrophied in both creatures 
physiologically since they no longer serve in respiration, and 
the denuded slits are subject to that variation which is the fate 
of all rudimentary organs. The first slit suffers most and is 
greatly reduced. In the two (or three?) specimens of Lepido- 
siren which have, up to date, been dissected, the edges of the 
slit seem to have grown together, while in Protopterus, though 
the slit is still open, itis very much reduced, being smaller than 
any of the other gill slits. I venture to say that no very large 
number of individuals of Protopterus have been examined with 
special reference to this point. However that may be, the 
coalescence of the walls of a degraded gill-slit is not a charac- 
ter of sufficient morphological importance to found a genus 
upon, except, perhaps, in the eyes of a confirmed genus builder. 
In both forms neither the first nor second gill-bars bear any 
gill membranes, but both possess an hyoidean demibranch 
(opercular gill rudiment). This gill is composed of a single 
row of gill leaflets as in Ceratodus. The third and fourth gill 
bars are provided with a double row of gill leaflets, while on 
the fifth arch is found only a single row of leaflets,a condition 
not obtaining in any other Dipnoan or Ganoid. 
When these animals were named, they were little known to 
science. If they had to be named as new discoveries to-day, 
and could both be studied together in so doing, most zoologists 
would include both animals in one genus, even if they did not 
group them as varieties of one species. 
I wish to call the attention of those anatomists who would 
insist upon keeping Lepidosiren and Protopterus distinct upon 
