1893.] On the Genera of the Dipnoi Dipneumones. 923 
the basis of the number of gill clefts left open irrespective of 
the fact that the number of functional gills is the same, to the 
fact that there are other fish with a variable number of gills 
which are considered by as good authority as Johannes Müller, 
to the extent of his knowledge of the case, to be mere varieties 
of one species. Müller found among the Bdellostomx from the 
Cape of Good Hope, individuals with 6 pairs of gills, others 
with an extra gill added to one side of the body, and still 
others with 7 full pairs of gills. 
I have ascertained that, taking all the Bdellostomids together, 
' they form a series in which the gill variation runs between the 
minimum of 6 pairs and the maximum of 14 pairs, or a DIFFER- 
ENCE BETWEEN THE EXTREMES OF 8 PAIRS OF GILLS, AND YET ALL 
THESE INDIVIDUALS NOT ONLY BELONG TO THE SAME GENUS— 
THEY BELONG TO THE SAME SPECIES ! 
THE RIBS. 
The number of ribs has been selected by Schneider as a 
character of generic as well as specific value. The possession 
of 56 ribs is held to be characteristic of Lepidosiren parodoza. 
Considering the small number of individuals examined, this 
cannot justly be said to be a settled fact. Schneider’s diagno- 
sis of 30 ribs for Protopterus amphibius, and of 35 ribs for P. 
annectens as a safe specific character, is, to say the least, ill- 
chosen, for the reasons that the number of ribs varies in speci- 
mens from the same locality, which have no other distinguish- 
ing characters save another variable, viz.: the presence or ab- 
sence of external gills, and for the further reason that some 
authors (Owen, loc. cit. p. 47) have counted at least 37 ribs in 
P. annectens. Schneider failed to define what structures he 
would have counted as ribs; but I assume he would admit all 
rib-like processes attached to the bare notochord between the 
pectoral and pelvie girdles as entitled to be named ribs irre- 
spective of questions of homology. THE NUMBER OF SUCH PRO- 
CESSES IS INCONSTANT IN Protopterus, but the extremes of varia- 
tion have not been definitely made out. The number prob- 
ably varies with age, but this is not certain. 
