MIDDLE BALA GROUP. 49 


Case and 
Column of 
Drawers. 
Reference to McCoy’s 
. : Names and References; Observations, &c. 
Synopsis: and Figures of Genera. 
Numbers and Localities. 

N.B. [Trinodus tardus of Barrande, though very 
Gk 



T. Caractaci, p. 144, 
var. elongatus, p. 145, 
T. radiatus, p. 146, 
TL. gibbifrons, p. 145, 
Pl. 18, fig. 14. 
T. latus, p. 145, 
PI. 1 &, fig. 15. 
Tretaspis fimbriatus, 
p. 146, 
Bip Wer ag: 6. 
Trinucleus, Llhwyd, Murchison. 

like ours has sufficient distinction. None 
of the Mid-European trilobites are the same 
as the British. 
Of all the 
curious genera of Trilobites, this is one of 
the most curious, so far as the head portion 
is concerned; for there is nothing peculiar 
about the body. A perforated border, which 
border consists of a double plate, surrounds 
the whole head, in front and sides: and 
is really built up of numerous fringing 
spines connected by their margins into one 
piece. There are no eyes (except some 
obscure traces in the subgenus Tretaspis), 
and scarcely a trace of a facial suture. The 
genus began with the earliest Bala rocks 
(Upper Cambrian) and must be said to 
have died out with them—only one or two 
straggling specimens occurring in higher 
beds, and this very rarely. On the con- 
trary, every member of the Bala rocks and 
every locality has more than one species 
of what might be called the “ Lace trilobite.” 
It could roll into a ball, like the woodlouse. 
Trinucleus concentricus, Eaton (Salter, Mem. 
Geol. Surv. Decade 7, Pl. 7, p. 5). The 
commonest of all the species from Ohio to 
Russia, it is liable to much variation, and 
has received many names. Some of the 
varieties are really worth notice, such as 
T. elongatus, Portlock. In attempting to 
separate these forms, the author of the 
Synopsis has entangled himself in the diffi- 
culties attending the study of fossils in 
cleaved and distorted strata. All those here 
noticed are mere states of preservation. 
T. gibbifrons represents the ordinary form 
in Wales, and the uncompressed Caradoc of 
Shropshire. Some of the specimens have 
fewer pores than others, &c. &. But the 
species is neatly distinguished by the form 
of the fringe, viz. flat and horizontal above, 

a. 133, as Z. Caractaci, 
Cheney Longville shales, 
and Horderley, Shropshire. 
Llansantfraid; Llechwedd, 
Llwydd; Bwlch-y-groes; 
Llanwddyn; Pwllheli, Ba- 
la; Llanfechan. 
As T. radiatus, N. of Tre- 
madoc (in beds of Bala age, 
supposed to be in upper 
Tremadoc slate!). p. 337. 
As T. elongatus (not of 
Portlock), Pwllheli. 
As T. gibbifrons, Dolydd 
Ceiriog waterfall in the 
Berwyns; Rhiwargor; Gar- 
nedd Fawr; W. of Bala: 
a. 134, Dinas Mowddwy; 
7 
