PTERYGOTUS PROBLEMATICUS. 87 



Antenna (pi. xii, figs. 7 — 10, Mem. Geol. Surv., Mon. I). — Fig. 10 is most probably 

 part of the stem, and shows the large and small plicae in perfection. Figs. 7 to 9 show the 

 large characteristic chelae, which can scarcely be confounded with those of any other species, 

 the teeth being so much elongated. Fig. 7 is the fixed claw, with a widely expanded and 

 largely dentate base. The shaft is parallel-sided (not tapering as in P. ludensis), and the 

 teeth long-lanceolate, the large one being much longer than the diameter of the shaft (in 

 fig. 7, fully three quarters of an inch long) ; the secondaries, three or four on each side of 

 it, with small teeth interspersed, all linear-lanceolate, erect and remote, not crowded at 

 their bases. In the fixed ramus they are either erect or (fig. 8) point forward a very little. 



The striae on the teeth are very fine and close ; somewhat oblique on the great tooth, 

 and more direct in the smaller ones. In P. gig as and P. hdensis they are coarser, and 

 the teeth broad. The great terminal mucro is as broad and long as the primary tooth, or 

 even longer, and is bent at right angles to the shaft. 



Sioimming-feet : Basal Joint (pi. xii, figs. 11 — 14, op. cit.). — Several fragments 

 have been found of the great basal joint, and one tolerably perfect from the Whitcliffe, 

 Ludlow (fig. 11). It shows a wide-expanded basal lobe, and the whole extent of the 

 serrate tip, with the usual number of teeth (thirteen, or rather twelve in this specimen), 

 in fig. 14 the upper tooth being obsolete. Fig. 13 a, from Ludlow, shows the full 

 number. 



The lobe in front of the teeth is arched and thickened in all the specimens (a character 

 in which this species differs widely from P. anglicus), and the second tooth is more than 

 twice the breadth of any of the others, conical, and but little curved ; the remaining teeth 

 are long, straight, narrow, and separated by about their width from each other in large 

 specimens. These elongate teeth are very distinctive of the species. I believe I am not 

 mistaken in referring Agassiz's figure of the Sphagodus tooth to this portion. 



Metastoma (pi. xii, fig. 15, op. cit.) is cordate-ovate, narrower at the bilobed end, 

 and has its greatest width below the middle, becoming angulated at that point. The 

 notch is deep, the lobes rounded (the base is broken off) ; surface marked with open 

 squamae, but only near the upper end and about the notch. This post-oral plate is the 

 broadest of any species known. 



Fig. 16 is a plate of the same nature as those found with P. ludensis, and is possibly a 

 thoracic or abdominal appendage, though, as no species are known .with any such attached, 

 its nature is quite doubtful. The entire form is better seen at p. 91 (Woodcut, Fig. 25), 

 viz. a lobed broad emarginate plate {d), in the wide notch of which is attached the trun- 

 cated sub-oval plate, b. 



Localities. — Upper Ludlow Rock, Whitcliffe, and many places near Ludlow (Ludlow 

 Museum and Museum of Practical Geology, Cabinets of Messrs. Lightbody, Cocking, 

 J. Harley, and A. Marston). Kendal, Westmoreland (Museum of Practical Geology). 

 Ludlow Bone-bed, Ludlow; Downton Sandstone of Bradnor Hill, Kington (Mr. R. 



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