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Show 1896.] MB. 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. Tomistoma has been noticed above. Osteolaemus, curiously, agrees with it. W e thus see that Metriorhynchus represents the most generalized condition, and that the recent Crocodilians, each departing 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 tbe 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 Osteolaemus 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 of Amphibia and Amniota (Phil. Trans, clxxxvii. 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. c. Centrum. cp. Capitular facet. ha. Hypapophysis. na. Neural arch. t. Tubercular facet (diapophysis). the batter's statement to be erroneous. W h a t 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 (t1), 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. ZOOL. Soc-1896, No. XLI. 41 |
