BRITISH FOSSILS. 



PLATE XIII. FIGS. 8, 12, 13, 15, AND 16. 



PTERYGOTUS AECDATUS. 



SPEC. CHAR. P. major, segmentis arcuatis, plicis semicircularibus 

 parvis, nee squamulis minutioribus intermixtis. 



The name is applied to a large and fine species, of which several 

 fragments occur in the Lower Ludlow Rock of Leintwardine, along 

 with the more common P. punctatus, Plates X., XI. It is clearly 

 distinct from that species, but except for the total absence of any 

 minute interspersed plicae, the body segments might be easily mis- 

 taken for those of P. problematicus, to which it is closely allied ; 

 and with it, in the same beds of Lower Ludlow Rock, occur 

 antennce (fig. 8), the obscure appendages (fig. 16), swimming feet, 

 maxillse, and other oral apparatus, differing specifically from those 

 of P. problematicus, and yet more distinctly separated from the 

 portions of P. punctatus, found in the same beds. Of these frag- 

 ments the body segment must receive the name, the other pieces 

 being only provisionally arranged with it. They all resemble the 

 corresponding parts in the Upper Ludlow species. 



Body Segments. Fig. 1 2 is clearly, from its shape, the second 

 body segment, seven inches broad and more than one inch and a 

 half deep. It is curved, and more oblique laterally than in P. anyli- 

 cus, the sides forming an angle of 65 with the base. The anterior 

 edge is much more sinuated than the posterior, owing to the deep 

 excavation to receive the first segment; but the central part is 

 strongly arched forward on both margins. The lateral anterior 

 process a is broken off, but enough remains to show it was pro- 

 minent. The sides are oblique, inclined forward at an angle of 80 

 from the posterior angle, which is rounded off. The margin is 

 crenulated, the prominent minute sculpture confined to the anterior 

 third, but continued more faintly over a large part of the segment. 

 (The sculpture in the thoracic segments of P. punctatus, Plate X. 



