HAPLODONTIDAZ—VERTEBRZ OF HAPLODON RUFUS. 575 
about. the middle of the series, when, with still increasing length, they also 
widen again and gradually assume the slight hourglass-like contraction, which 
is more conspicuous in the lumbar series. The centra all bear costiferous 
demi-facets, one at each end, to the 9th, which has only one such demi-facet 
on the fore end, and none on the other (as well as can be determined in the 
dried state of the bones examined); the last four (10th to 13th) have full 
facets upon their fore ends. The spinous processes of the anterior half- 
dozen dorsals are long, slender, compressed, tapering to a knobbed point, 
excepting the 1st one, which ends acute, and is abruptly shorter than the 
next; the 2d to 6th are subequal and longest; all these slender acute spines 
incline strongly backward, and are packed closely in the concavity of this part 
of the spinal column. On the 7th vertebra, the character of the spinous 
processes begins to change; they shorten rapidly in vertical length, and at the 
same time lengthen horizontally, becoming erect and laminar instead of 
acuminate, thus merging insensibly into the vertically short, horizontally long; 
rectangular, plate-like spines of the lumbar region. 
The ‘transverse ” processes of the dorso-lumbar vertebree offer a means 
of distinguishing between the two series as readily as does the presence of 
true ribs in one and their absence in the other, whether we pay attention 
to the homologies of the various elements of which these processes are re- 
_spectively composed, or simply regard their physical appearance. The dorsal 
diapophysis proper, by which I mean that portion of the complex “trans- 
verse” process which bears a facet for articulation with the tubercle of a rib, 
is most projecting on the 1st dorsal, and bears a cupped facet; this process 
regularly diminishes in length, and in the concavity (soon lost) of its facet, 
to the 10th vertebra, and is entirely wanting, to all appearance, on the 11th to 
13th vertebrae, with which the corresponding ribs have no connection except 
by means of the respective centra. From the upper surfaces of these 
diapophyses, excepting the 1st one, springs another series of processes, which 
begins with the 2d dorsal as a simple spur, directed backward, upward, and 
outward ; these rapidly increase in size with successive vertebra, and with 
the 6th acquire a new character, becoming expanded and plate-like, and 
developing an anterior spur as well as retaining the original posterior one. 
The formation grows more distinct on succeeding vertebrae to the 10th. A 
decided excavation of circular shape lies on the under side of this plate ; the 
anterior corner overlies the pre-zygapophysis of its own vertebra, and the post- 
