FEB., 1906. CARAPACE AND PLASTRON OF BASILEMYS SINUOSUS. 251 
posteriorly and lies opposite the suture between pleurals -v11 and 
vi. A ninth irregularly rounded plate intercolated between the 
last pair of costals may be regarded as a post-neural. 
The pleural plates extend only about two-thirds of the distance 
from the neural suture to the margin of the carapace. Their articu- 
lation with the neurals has been described in the preceding para- 
graph. Distally they articulate with the marginals, breaking joints 
in a mosaic pattern. Pleurals 1 to m1inclusive are directed obliquely 
forward. Pleural tv stands at a right angle to the median line. 
From this point the remainder of the series becomes more and more 
directed obliquely backward until the last pair conforms to the wide 
A-shape of the first pygal. Pleural 1 is much the broadest of the 
series, articulating anteriorly with the nuchal and peripherals one 
and two. Distally it abuts the whole mesial border of peripheral 
three and a small anterior portion of four. Pleural 1 is long and 
narrow, meeting only two-thirds of peripheral four. Pleural 111 is 
widest at the distal end, articulating antero-laterally with the fourth 
and laterally with the fifth peripheral. Pleural iv is uniform in 
width, and has a distal articulation similar to the perceding. Pleural 
v is slightly expanded toward the extremity and presents an almost 
equal surface to marginals six and seven. The suture between Pleu- 
rals v and vi is unusually sinuous. The latter element is noticeably 
narrower and has its distal articulation similar to the preceding. 
Pleural vir is shorter, and much narrower at the mesial end. It 
articulates distally with peripheral eight by a short suture, but chiefly 
with nine. Pleural vit is shortest and smallest of the series. It 
_ arises from the eighth and ninth neurals, and is more uniform in 
width than the preceding. It meets peripheral nine in a short 
antero-lateral suture as well as half the mesial surface of peripheral 
ten. 
The first pygal plate has the form of a wide A. Its lateral wings 
are co-extensive with the last pair of pleurals, with which they articu- 
late anteriorly. Laterally they abut a third of the mesial surface 
of peripheral ten. The posterior surface is concave to receive the 
rounded surface of the succeeding element. The second pygal is a 
wide irregular figure, convex on the anterior surface and bounded 
by three concave facets posteriorly. These facets articulate with 
the eleventh pair of peripherals and the third pygal. Laterally this 
bone also presents a small pair of surfaces to the postero-lateral faces 
of the tenth pair of peripherals. The third pygal is not more 
than half as large as the second and is sub-hexagonal in outline. 
