LIMULID^. 
PROTOLIMULUS, Packard. 1886. 
Protolimulus Eriensis. 
PLATE XXVI, PIGS. 1, 2. 
PrestwicMa Eriensis, H. S. Williams. Amer. Jour. Science, vol. xxx, Third Series, p. 46, fig-s. 1-3. 188,6. 
Protolimulus Ei'iensis, Packard. Mem. Nat. Acad. Sciences, p. 150, tigs. 11-13. 1886. 
The type specimen of this interesting species is an impression of the lower 
surface of the body, in very high relief, upon a block of fine-grained, compact, 
olive-gray sandstone. Its condition of preservation is such that the removal 
of the substance of the tenuous test, during the process of fossilization, and 
the infiltration of the sediments into the internal cavaties of the telson, genal 
and abdominal spines, has left these parts standing out conspicuously, while 
over the central portion of the fossil there are various impressions which appear 
to be those of the appendages, and indicate something of the structure of the 
ventral surface of the animal. In the original description of the species, these 
characters have been carefully studied, and have undoubtedly been given their 
full importance, for the medium in which the fossil is preserved is not of 
such a character as to retain, with perfection, such delicate impressions as the 
appendages of this animal would have made, and it is possible that the appear¬ 
ances described may to a certain degree be fortuitous or mechanical, and with¬ 
out structural relation to the fossil itself; there is however a distinct symmetry 
in their arrangement, and it is important that the view of their mechanical 
origin be subordinated to that of their organic character. 
