PTERYGOTUS ARCUATUS. 89 



P. problematicus, to which it is closely allied ; and with it, in the same beds of Lower 

 Ludlow Rock, occur antennae, the obscure appendages (figured in our Woodcut, Fig. 25, 

 p. 91), swimming-feet, maxillae, and other oral apparatus, differing specifically from those 

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

 Eurypterus) punctatus found in the same beds. Of these fragments 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 (pi. xiii, fig. 12, Mem. Geol. Surv., Mon. I). — This specimen 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. anglicus, 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 is broken 

 off, but enough remains to show it was prominent. 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 rest of the segment. 



A specimen, crushed longitudinally, shows that the species was rotund in section, as in 

 P. (now Eurypterus) punctatus and others. 



Antenna. — In all probability, pi. xiii, fig. 8, Mem. Geol. Surv., Mon. I, represents the 

 antenna of this species. Its resemblance to those of P. problematicus is very close. The 

 shaft is linear, the long end turned abruptly up, and the teeth straight, narrow, and 

 remote, as in that species ; but the chela is much more slender, three inches and a half to 

 four inches long, and the larger central tooth is scarcely longer than the diameter of the 

 shaft itself, while the secondary teeth, some of them at least, approach it more nearly in 

 size. The tooth at the base of the large terminal mucro is appressed against it, and the 

 mucro itself (pi. xi, fig. 3, op. cit.) is sometimes oblique. All the teeth are finely striate, 

 the striae tending obliquely backward on the principal teeth. There are numerous sharp, 

 conical, minute teeth between the secondaries. 



Fig. 21.— The basal joint of an endognath of Pt. areuatus, I Fig. 22.— Mandibular border of one of the endognaths 

 Salter. of Pt. areuatus ? 



Both specimens from the Lower Ludlow Rock, Leintwardine, Shropshire. 



Endognaths. — Most probably, pi. xiii, fig. 15, Mem. Geol. Surv., Mon. I, represents 



