254 Fietp CotumBiANn Museum — Geo oey, Vor. III. 
union with the pubic process. From the femoral notch to the median 
line the margin is elevated to form a sharp ridge, deeply pitted on 
the free surface. 
The dermal smelds of the plastron are very complex in arrange- 
ment. Theintergulars are similar on the inferior surface to those 
of B. vartolosus, but superiorly they are extended to cover the pro- 
truding gular process. Between them the median sulcus twice crosses 
the median suture. The gulars are long and narrow, and meet at the 
median line. The humerals are relatively smaller than in B. vario- 
losus. They present for union at the median line a surface barely 
a half-inch in length. The pectoral shields as a pair are similar in 
outline to those of the species cited, though they extend somewhat 
farther backward mesially. Between them the median sulcus de- 
parts from the median line in a series of meanderings in which it 
crosses the median suture five times. In the abdominals it follows 
almost parallel with the suture making a single digression near the 
posterior border. The abdominals send backward a pair of peculiar 
narrow processes between the inguinals and femorals to the border 
of the femoral notch. The femorals are sub-quadrangular in outline, 
extending laterally to the border of the femoral notch. In the anals 
the median sulcus presents the most fantastic tracery, crossing the 
median suture in a series of wide loops, departing from it, in one in- 
stance, nearly two inches and finally returning to it at the posterior 
margin. On account of portions missing at the lateral angle of 
the carapace it cannot positively be determined whether the 
marginals are divided into an inframarginal series. From the fact 
that no evidence of a dividing sulcus can be made out on either side, 
as well as the opposite position of the vertical sulci on each side of 
the gap, it is assumed that the series is not divided into marginals and 
inframarginals, respectively. 
From the narrow lateral extremities of the pectorals radiate 
three wedge-shaped shields. The anterior and smallest is the axillary 
shield which overlies the axial buttress and extends upward along 
the free margin of the carapace to join the second nuchal. The 
other shields radiating from this point are the fourth and fifth 
marginals. The sixth marginal is very broad at its ventral 
border, joining nearly the whole lateral surface of the abdominal 
shield. Two pairs of shields converge at the postero-lateral 
angle of theabdominals. The most anterior is the seventh mar- 
ginal, which narrows mesially almost to a point. Back of this lies . 
*Proc. Acad. Nat. Sci. Phila. 1876, p. 257. 
