CRUSTACEA. 
155 
furrows appear to be carried for a considerable distance posteriorly over an 
area that may have been the continuation of this plate. Admitting that it 
was thus produced, there is evidence that it was divided by a transverse 
furrow or suture, making the analogy of its structure with that of the 
thoracic plate in Limulus very striking. 
Abdomen. The posterior surface of the body bears a transverse row of eight, 
possibly ten longitudinal ridges, which may be the impressions of elevations 
on the surface of the abdominal area. These correspond in number with, 
and lie immediately in front of the stout spines fringing the postero-lateral 
margins, although the inner pair of spines lies so close against the base of 
the telson as to have left only very faint impressions. 
Telson very stout at its base, tapering to a blunt extremity, and having a length 
equal to nearly two-thirds that of the cephalothorax. 
Dimensions. Axial length 100 mm.; width 58 mm. Length of telson 
32 mm. 
Observations. The affinities of this fossil, as far as it is possible to judge, are 
distinctly limuloid, as pointed out by Professor Packard {loc. cit.), who has 
proposed the generic term Protolimulus to include this form. Both Williams and 
Packard ascribe to the fossil seven abdominal segments, including the telson; 
we have, however, been able to find evidence of but six, though it may be 
reasonable to assume that the first or first two of these segments were 
concealed by the appendages of the animal. The character of the dorsal 
surface is a matter of conjecture, but as far as the specimen enables us to form 
a conception of it, it seems to be closely similar to that in the genus Neolimulus, 
of Woodward {N. falcatus, from the Lesmahagow deposits of Lanarkshire), in 
which the abdomen is composed of nine segments besides the telson, which are 
regarded by Woodward as unanchylosed; it is probable that this is likewise 
their condition in Protolimulus. 
Distribution. Chemung group, LeBoeuf, Erie county, Pennsylvania. 
