BRITISH FOSSILS. 



PLATE I. FIGS. 1-12. 



SECTION 1. 

 PTEEYGOTUS BILOBUS. 



P. 8-uncialis, sublcevis, capite semielliptico, corpore abbreviate antice 

 latiori, caudd oblongd carinata emarginata. 



SYNONYM. Himantopterus bilobus, SALTER, in Quart. Journ. Geol. Soc. 

 vol. xii. p. 29. fig. 1. ; also " Siluria," 2nd edition, p. 155, foss. 21. PAGE, 

 in Advanced Textbook, p. 135, fig. 1. 



We have more perfect materials for this species than for any of 

 the rest, above twenty specimens, many of them full grown, and 

 showing all the segments ; in some the head with its elongate eyes 

 and few-jointed antennas ; the long palpi in others ; two show the 

 serrated jaw feet beneath the carapace with the swimming joints 

 attached ; the post-oral plate is in situ in another ; and there are 

 numerous detached specimens of all the appendages except the 

 palpi, of which last we should know but little but for the ex- 

 planation afforded by the next described species. 



The geological position of this and the other Pterygoti from 

 Lesmahago has been fully given by Sir R. I. Murchison, our Director- 

 General, in the 12th volume of the Quarterly Journal of the Geological 

 Society, p. 23. . The occurrence with them of a small spiral shell and 

 a Lingula, identical with those of the Downton Sandstones of 

 Shropshire, justifies the reference of the strata to the age of the 

 Uppermost Ludlow Rocks, while not one of the species is identical 

 with those of the border counties of Wales, either in the Ludlow 

 Rocks or in the Passage Beds which immediately overlie them. 

 This fact is remarkable, and may serve to indicate the probability 

 of a vast number of species yet to be discovered. 



