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 transv< 

 furrow or suture, making the analogy of its structure with that of the 

 thoracic plate in Limulus very striking. 



Abdombn. The posterior surface of the body hears a transverse row of eight, 

 possibly ten longitudinal ridges, which may he 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. 



Telsox 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 (he 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 he 

 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 Neolitnulus, 

 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. 



