1896.] MR. G. A, BOULENGER ON SCHLEGEL’S GAVIAL. 633 
the second is deeply bifurcate, the tuberculum ligamentous, and 
attached to two processes on the centrum of the atlas. 
ali has been noticed above. Osteolemus, curiously, agrees 
with it. 
We thus see that Metriorhynchus represents the most gene- 
ralized condition, and that the recent Crocodilians, each depart- 
ing in its way from the primitive type, cannot be arranged in a 
continuous series in this any more than in several other parts of 
their structure. Whilst more generalized in respect to the second 
rib} than the true Crocodiles, the Alligator is more specialized in 
the more aberrant position of the first rib; the Gavial agrees 
with the Crocodile in the position of the first rib, and with the 
Alligator and Caiman in the strong bifurcation of the second ; and 
Tomistoma and Osteolemus present the highest specialization in 
the condition of the second rib with rudimentary tuberculum. 
P.S. (June 18, 1896).—Two days after the reading of my paper, 
I received Dr. Gadow’s memoir on the Vertebral Column ot 
Amphibia and Amniota (Phil. Trans. elxxxvii. B. pp. 1-57). In 
this he gives an account and a diagrammatic figure of the atlas 
and axis of Metriorhynchus, which differ entirely from what I have 
observed. I at once re-examined the specimens, and particularly 
that described by Hulke and figured by Dr. Gadow, and find 
Fig. 2. 
Atlas and axis of Metriorhynchus. 
na. Neural arch. 
c. Centrum. 
t, Tubercular facet (diapophysis). 
cp. Capitular facet. 
ha. Hypapopbhysis. 
the latter’s statement tobe erroneous. What is figured as the first 
centrum is a portion of the first neural arch, the posterior portion 
of which has passed, on the figure, into the second vertebra; the 
tubercle (#'), to which allusion is made, is on the neural arch. I 
append (fig. 2) a corrected sketch of the specimen figured by 
Dr. Gadow. 
1 Another character in which Alligator is more generalized than Caiman 
and Crocodilus exists in the proatlas, the arches of which are distinct or show 
at least a trace of separation, which is not to be found in the other genera, even 
in quite young specimens. 
Proc. Zoou. Soc.—1896, No. XLI. 41 
