No. 462.] CRABS OF GAY HEAD MIOCENE. 383 
These show many points of structure not heretofore described. 
The material is in the museum of the Boston Society of Natu- 
ral History, and is referred to by number. The material at the 
Museum of Comparative Zoölogy at Cambridge was also studied 
and is also referred to as well as one or two specimens in the 
teaching collection of the Paleontological Department of Har- 
vard University. 
Archzoplax signifera Simpson. 
Archeoplax signifera Stimpson, Boston Journ. Nat. Hist., vol. 7, 
no. 4, April, 1863, p. 584, pl. 12, figs. 1-4; Dall, Amer. 
Journ. Sci., vol. 48, 1894, p. 297; Packard, Proc. Amer. 
Acad. Arts and Scis vol. 36, no. 1, July, 1900, p. 7, pl. 1, 
fig. 4, pl. 2, figs. 1-3. 
Carapace.— In the specimens the length of the carapace 
varies from 1 to 2.5 inches, in greatest breadth from 1.2 to 2.75 
inches, and in posterior breadth from 0.75 to 1.8 inches. The 
superior outline along the median antero-posterior line is decid- 
edly curved as noted by Stimpson. This is shown in an outline 
side-view of a typical carapace (Pl. 1, Fig. 1). A similar view 
in the median line (Pl. r, Fig. 2) shows at the slope at the sides 
and the depressions at each side of the median portion. The 
surface of the carapace is smooth, finely punctate or granular, 
the coarser granulation being in definite portions of the central 
region as well as of the anterior and lateral regions. The color 
pattern of the carapace is very well made out in several speci- 
mens. In the great majority of the specimens it is shown by a 
difference in smoothness and in luster of the surface, but may 
be seen as black markings against d dark gray background, as 
in Pl. 2, Fig. 3, or best of all on the under side of the upper 
surface as black markings on a very light brownish white back- 
ground (Pl. 2, Fig. 4). Here the. markings stand out with 
remarkable clearness. There is considerable variation in the 
markings of this species but all follow the same general pattern. 
The central lunate markings are important as a means of orient- 
ing any large or small part of a specimen of this species which 
