102 Frederick Chapman : 



difficult to secure good specimens for description. The numerous 

 carbonaceous nodules and twig-like remains found there are to 

 be generally attributed to that genus ; the former representing 

 the internal casts of the carapace, the latter the abdominal 

 segments, the telson and lateral spines. 



One of the most important fossils noticed here is Xiphidio' 

 caris, a generic type whose species was first described by Salter, 

 and later by Jones and Woodward under the name of Xipho- 

 caris. It has hitherto been collected only from the Lower 

 Ludlow beds of England, where it is exceedingly rare. It 

 appears to be related to the ceratiocarids. 



(?) VliRMES ErKANTIA. 



Genus — Trachyder>/ia, Phillips. 



This genus was founded to include some more or less prob- 

 lematic fossils which occur in the Ordovician (Caradoc beds) 

 and the Silurian (Woolhope Limestone and Upper Ludlow) in 

 England. In his original description^ John Phillips says : " It 

 may be ranked anionoj Serpulidae, having a meiubraiious 

 covering, and a remarkable, though not quite regular, alterna- 

 tion (due, perhaps, to a peculiar spirality) of the successive 

 laminae of growth. There are, however, some appearances in the 

 specimens of T. coriacea, which may possibly be adduced in 

 favour of a reference of this fossil to a different group of 

 Annelida." 



Good examples, referable to the above genus, occur very 

 frequently in the sandy mudstones of the Melbournian division 

 of the Silurian, particularly near Melbourne, and also spar- 

 ingly in the mudstones of later Yeringian age in the Upper 

 Yarra district. The additional evidence of structure and habit 

 furnished by some of the specimens now described, shows that 

 the tubular lining or strengthening secretion of the walls of the 

 burrow may have been, in at least one of the Australian species,, 

 partially calcified, or possibly of the nature of a mud tube 

 similar to that made by the polynoids of the present day. The 



1 .>fem. Geol. Siirv. Gt. Riit., vol. ii., i)t. i., 1848, !>. :m. 



