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BRITISH FOSSIL CRUSTACEA. 



Antenna. — These resemble in general form those of P. anglicus, but have a more 

 slender shaft, tapering more quickly and narrower and with more conical teeth. The 

 teeth are intermediate in form between the species above mentioned and P. problematicus, 

 the central one being long- lanceolate, and the secondaries narrow, conical, and with 

 coarse striae. The base of the fixed claw is furnished with a set of stiff spines, as in 

 P. problematicus, but the whole chela is proportionably much shorter. 



Endognaths. — Of these there seem to be three pairs, as in P. anglicus, and of very 

 similar shape. The joints of the palpus, like those of P. gigas, have a squamose ridge, 

 along each side, and the ends of the joints are bilobed. The second joint is three and a 

 quarter times as long as broad. This is nearly the proportion in P. anglicus, where it 

 is three times the breadth. (See Woodcut, below, Pig. 16.) 



The other pairs of jaws have their anterior margin more curved, and the teeth set on 

 a more convex edge than in P. anglicus. The first tooth is set more backward, thick, 

 and curved at the base, and all are more curved than in the Scotch species. 



The Post-oral plate may belong either to this or to P. gig as (see Woodcut, Fig. 18, 

 p. 84). 



Base of Swimming-foot (PI. XVI, fig. 9). — These portions are very characteristic in all 

 the species. In this the shape most nearly resembles that of P. gigas, and the teeth are 

 short and blunt, as in that species, but the neck is shorter. From P. anglicus, the 

 shorter form, the short neck, blunt teeth, and convex upper lobe overhanging the teeth 

 distinguish it ; but the sculpture raised into thick, prominent, boss-like plica? is almost 

 identical. The lower edge is tuberculate, and even spinous ; our figure does not show 

 this part. A little comparison of this specimen with P. anglicus will show that both in 

 the upper or front edge and on the lower or hinder edge the terminal lobe is more 

 prominent in P. ludensis. 



Fig. 15. — Mandibular border of ectognath of Pterygotus ludensis, Salter, from Mr. Lightbody's Cabinet. 

 ,, 16. — An endognatb of PL ludensis, with its palpus. Museum Pract. Geology. Both specimens from the 

 Basement-beds of the Old Red Sandstone, Ludlow Railway, Ludlow. 



