XIPHOSURA. 

 LIMULID^E. 



PROTOLIMULUS, Packard. 1886. 

 Protolimulus Eriensis. 



PLATE XXVI, FIGS. 1, 2. 



Prestwichia Eriensis, H. S. Williams. Amer. Jour. Science, vol. xxx, Third Series, p. J'!, figs. 1-3. 1885. 

 Protolimulus Eriensis, Packard. Mem. Nat. Acail. Sciences, p. 150, figs. 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. 



