386 THE AMERICAN NATURALIST. | (Vor. XXXIX. 
Of the posterior four pairs of legs we have with the help of 
one specimen obtained in 1904 (Pl. 2, Fig. 2), a knowledge of all 
the parts. This specimen had the last four joints of a single 
leg very well preserved. The main characteristic of these 
appendages is the great length of the fourth joints. These 
joints are considerably flattened in some cases but usually 
appear in cross section as shown in Pl. 2, Fig. 13. 
Certain of the specimens preserved in the concretions show 
the internal characters very well. The doubly triangular skele- 
tal mass shown in Pl. 2, Fig. 5, is often seen perfectly preserved. 
The divisions of the posterior part of the body are also seen in 
the same figure. In rare cases the gills are found lying in their 
cavities. In one case a small piece was taken out, softened and 
mounted. In this condition it showed the tubes and something 
of the structure of the gill. Apparently it was simply dried and 
not in any degree impregnated by mineral matter. A small rod- 
like mass is often seen when the front is broken away exposing 
the interior. 
Altogether it seems that we now have a very fair knowledge 
of this Miocene species. In PI. I, Fig. 3, is given a restoration 
of this species from the specimens studied. 
Cancer proavitus Packard. 
Cancer proavitus Packard, Proc. Amer. Acad. Arts and Sci., vol. 
36, nö. 1, July, 1900, p. 4, pL n Bes 1-2, ‘ 
Of all the specimens examined there seems to be but one 
which is in any way referable to this species. This specimen 
from the white leached layer already mentioned, consists of the 
cast of the sternum, abdomen, and outer maxilliped of a small 
female individual. Its main characters are shown in Pl. 2, Fig. 
14. From a study of the type the specimen is referred to this 
Species as it seems to be a Cancer and is from the same bed as 
was the type of this species. The type was a male and this is 
in all probability a small female of the same species. It will be 
at once seen that it cannot be referred to Archzoplax, which has 
