666 SILURIAN TRILOBITES OF NEW SOUTH WALES, V., 



thorax; axis tapering very gradually from before backwards, and 

 terminating in a rather fine point; annulations thirty or more^ 

 the first only continuous, and, together with the next three or 

 four succeeding, tuberculate; central area distinct, bearing seven 

 or more tubercles, five of which are usually very conspicuous, 

 only the first annulation decidedly arched, the others flat above 

 with steep sides; pleural lobes very moderately geniculate, ante- 

 riorly about twice as wide as the anterior width of the axis; 

 annulations are of the usual Encrinurid character, and are twelve 

 in number. 



Ql)s, — This is a robust species, and reaches a length of two or 

 more inches. Its cephalon in general form and tubercidation 

 approaches more nearly to that of E. variolaris than to any other 

 European member of the genus, but its relatively enorpious 

 pygidium separates it from this species. The coarse cephalic 

 tuberculation at first sight might cause it to be mistaken for 

 E. hoivninge7isis; but the larger size, more acutely conical nature, 

 and conspicuous granulation of the tubercles of E. siherdalensis 

 easily separate it from that species. The general form of the 

 cephalic shield, and larger pygidium with the greater number of 

 pleural segments of E. silverdalensis renders its distinction from 

 E. hoivningensis and other species we are acquainted with very 

 simple. The pygidium is only approached in size by that of 

 E. etheridyei, Mit.; but other features in the two widely differ. 

 In its inconspicuous neck-furrow, coarse tuberculation of the 

 cephalon, the strong tubercles on the central space of the pygidial 

 axis, it resembles the typical Wenlock forms, E. pu7ictcUus, Brtin., 

 and E. variolaris, Brong.; but the tubercles in both instances 

 are of a different type. The genal angles are not produced into 

 spines, nor the pygidium into a telson as in E, punctatus. This 

 trilobite was evidently very local in distribution, and restricted 

 stratigraphically, for it is only known from the Lower Trilobite 

 Bed of the Bowning Series ( = Hume Beds) at the one locality. 

 It is there associated with MuGophyUutn crateroides, Eth. fil., 

 Heliophyllum yasseiise, Eth. fil., Rhizophyllum interpunctatum,, 

 De Kon., and other corals typical of the Bowning- Yass beds. 



