)
(FIGURE 305. Third and largest pre-molar (lower jaw) of Plagiaulax Becklesii,
magnified 5 1/2 diameters, showing 7 diagonal grooves.)
(FIGURE 306. Plagiaulex Becklesii, Falconer. Middle Purbeck. Right ramus of
lower jaw, magnified two diameters.
a. Incisor.
b, c. Line of vertical fracture behind the pre-molars.
pm. Three pre-molars, the third and last (much larger than the other two taken
together) being divided by a crack.
m. Sockets of two missing molars.)
The largest pre-molar (see Figure 305) in the fossil genus exhibits in like
manner seven parallel grooves, producing by their termination a similar serrated
edge in the crown; but their direction is diagonal-- a distinction, says Dr.
Falconer, which is "trivial, not typical." As these oblique furrows form so
marked a character of the majority of the teeth, Dr. Falconer gave to the fossil
the generic name of Plagiaulax. The shape and relative size of the incisor, a,
Figure 306, exhibit a no less striking similarity to Hypsiprymnus. Nevertheless,
the more sudden upward curve of this incisor, as well as other characters of the
jaw, indicate a great deviation in the form of Plagiaulax from that of the
living kangaroo-rats.
Pages:
589
590
591
592
593
594
595
596
597
598
599
600
601
602
603
604
605
606
607
608
609
610
611
612
613