428 Notices of Memoirs — H. 8. Williams — On a Fossil Limulus. 



they constitute the distinctive characters of the species, as far as 

 these can be made out from the specimen. 



The under side of the body presents three well-defined tracts, 

 viz. the cephalic shield, which is evenly rounded in front, and is 

 laterally prolonged backward into two genal spines, which are 

 nearly parallel with the axis of the body, and reach nearly to a 

 point opposite the posterior margin of the buckler. The cephalic 

 shield along the median line is about a third the length of the body ; 

 the space between the posterior margin of the cephalic shield and 

 the anterior margin of the buckler, containing the region of the 

 mouth and the gnathopods, and the thoracico-abdominal buckler, 

 marked over the surface by longitudinal ridges, and by marginal 

 spines, and terminating in a long stout telson. Traces of the 

 gnathopods are seen, as also traces of the foliaceous appendages of 

 the posterior feet, but in too imperfect condition for exact delineaticm. 

 Just anterior to the position of the mouth is seen a shield-like 

 elevation upon the edge of the cephalic shield, which has the 

 appearance of an hypostoma. The condition of the specimen is not 

 such as to give absolute certainty to this interpretation, though the 

 symmetry of its form is strongly in favour of it. It is possible that 

 it is merely outlines upon the surface, produced by crushing during 

 fossilization. There are faint indications of joints on each of the 

 anterior set of gnathopods. 



Along the centre of the thoracic region, there is a flattened 

 depression, traversing longitudinally from the anterior edge of the 

 plate, backward to the middle of the telson. 



The terminal portion of the telson is evenly rounded. Each side 

 of the median line of the buckler there are visible four clearly- 

 defined marginal spines ; there were probably more of them — six, 

 I have supposed, but concealed in the specimen by the filling 

 between the buckler and genal spines. 



There are also four rounded, longitudinal ridges on the buckler 

 each side of the flattened depression ; these begin abruptly near the 

 anterior margin of the buckler, and run almost directly backwards, 

 tapering to a slender point near the margin of the buckler. 



At the anterior margin of the buckler is a narrow plate, divided 

 into a median and two lateral parts, which appears to be separated 

 from the buckler itself by a distinct furrow. Laterally this plate 

 appears to curve inwards and lies below (within) the surface of the 

 buckler, and the median portion extends forward to a blunt point. 

 I have interpreted this as probably representing the consolidated 

 lamellar appendages of the " first and second " thoracic segments of 

 Eurypterus as defined by Hall in Paleontology of New York (vol. 

 iii. p. 398).i 



The telson is nearly two-thirds the length of the body, is flattened 

 at the base, but nearly cylindrical and tapering to a blunt point at 

 the extremity. 



^ If these indications are the remains of lamellar appendages, they are like those 

 of Limulus, and may be compared with the generative plate and branchigerous 

 thoracic appendages of the Xiphosuea. — H. W. 



