160 



SILURIAN TRILOBITES. 



The caudal shield much resembles that figured as A. laticostat-us, but it differs 

 from it in the greater width of the tail, and especially of the axis, which has continuous 

 non-interrupted furrows across it; and also in the undulated, convex and not flat, ribs 

 of the limb. The caudal fascia, too, is twice as • broad. 0. corndensis is, more- 

 over, a larger species, and must have measured full five and a half inches in length 

 when perfect. ; ' 



Fig. 32. 



Oyygia corndensis, Murchisoii. 

 Very perfect caudal portion, from the Lower Llandeilo Flags, Builth, Radnorshire (Mus. P. Geology). 



Fig. 33. 



Tail two and a half inches long and four and a half inches wide, semicircular, 

 gently convex all over, with the conical axis broader than in A. laticostatus, not one 



fourth of the whole width of the tail, and tapering gradually 

 backwards to a very obscure apex, which reaches to five 

 sixths of the whole length. It has about eight or ten rino-s, 

 a httle more curved than in the last species, not quite direct 

 across, but not interrupted in the middle by any line of 

 connected points. The axal furrows are shallow, and not 

 very well defined in this fossil, while in the last they are deep 

 and strong. 



The sides show a broad gently convex surface, marked 



by eight gently undulating convex ribs, the furrows between 



which are shallow, and curved backward nearly to reach 



the margin, which is a little concave only just at the end 



of the tail, not on the sides. The furrows seem to radiate just as in the last species, 



but are more regularly curved and not bent back so suddenly as in that species. The 



O. corndensis, Murch. 



Small specimen from felspathic 

 rock, probably a boulder. The 

 late Mr. Pardoe's collection. 



