92 



BRITISH FOSSILS. 



distinctive of the species. I believe I am not mistaken in referring 

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



Metastoma (Plate XII. fig. 15, Plate XIV. fig. 19) is cor- 

 date-ovate, narrower at the bilobed end, and has its greatest 

 width below the middle (our figure does not express this well), 

 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. 1 6 is a plate of the same nature as those found with P. lu- 

 densis, and is possibly a thoracic or abdominal appendage, though, 

 as no species are known with any such attached, its nature is quite 

 doubtful. The small crenate fragment, fig. 17, probably belongs 

 to it ; a similar piece is attached at c to fig. 16. [The entire form is 

 better seen in P. arcuatus, Plate XIII. fig. 16, viz., a lobed broad 

 emarginate plate (d), in the wide notch of which is attached the 

 truncated sub-oval plate a, &.] A more perfect specimen is here 

 added in a woodcut, showing the thickness of the plate on the one 

 side of it. The obscure converging lines ending in serrations on the 



FIG. 12. 



Pterygotus problemati- 

 cus, Ag., thoracic or 

 abdominal append- 

 age ? nat. size. 



Comus Wood, Ludlow, 

 in Upper Ludlow Hock 

 (Cabinet of Mr. J. 

 Harley, King's Coll.) 



border are exhibited on one surface ; on the opposite, the oblique 

 close plicse running into parallel lines towards the margin, very 

 like the segments of a feather. 



The base a a is much extended on each side, and in this respect 

 seems to be different from the figure above quoted, Plate XIII., 

 which probably belongs to P. arcuatus. 



Localities. UPPER LUDLOW ROCK, Whitcliffe, and many 

 places near Ludlow (Ludlow Museum and Museum of Pract. Geo- 

 logy 5 Cabinets of Messrs. Lightbody, Cocking, J. Harley, and 

 A. Marston.) Kendal, Westmoreland (Museum of Pract. Geology). 



