352 F. R. Cowper Reed — The Genus Trimicleua. 



but as the iuner plate bends up immediately behind the second ridge 

 it is probable tl>at this one represents the girder of other species. 



In. the allied species T. ornatus and T. Guldfussi from Bohemia there 

 is seen to be no distinguishable girder, the ridges being equal and the 

 lamella not bent, as Barrande figured.' 



In T. Nicholsoni ^ the girder is strongly developed inside the second 

 row (PI. XVIII, Fig. 6), and the same position is found in specimens 

 of T. seticornis from Rhiwlas, Norber Brow, Applethwaite, Sholeshook, 

 Redhill, etc. 



In T. Biichlandi from Girvan the girder is equally well developed, 

 and has the same position, but this is not the case in immature 

 individuals in front where only one row of pits is present (see sequel). 

 The same peculiarity is noticeable in specimens of T. seticornis from 

 the Trinucleus Shales of Nitsjo, Dalarne. 



In T. Murchisoni there is a well-marked girder inside the series of 

 radial grooves on the outer band, each of which holds three pits 

 in a line (PI. XVIII, Fig. 11). It is similarly situated, but narrower, 

 in T. Ether idgei. 



The position of the girder inside the first concentric row is found in 

 T. Portlochi from Tyrone, as is well shown in B. Smith's figure,^ and 

 the type-specimen of Portlock's 1\ elongatus^ likewise has the girder 

 in the same position. 



T.favus, Salter, has the strongest of its concentric ridges inside the 

 first row (PI. XVIII, Fig. 9), and the same is noticeable in American 

 specimens of T. concentricus from the Utica Slate. 



In T. fimhriattis the lower surface of the fringe (PL XVIII, Fig. 10), 

 which is quite unlike the upper one in the character of its pitting 

 (see sequel), has a broad outer band with only one marginal row of 

 pits and no radial grooves ; inside this row the outer band is smooth 

 and devoid of pits to the line of bending, which is sharp but not 

 marked by any thickening or distinct girder. 



T. hibernicus has a somewhat similar wide smooth flat space on the 

 outer band behind the two rows of small sunken radially arranged 

 pits in weak sulci (PL XVIII, Fig. 2) ; the junction with the inner 

 band is liliewise angulated and sharply defined, but without any 

 raised ridge or thickening. 



EXPLANATION OF PLATE XVIII. 



Fig. 1. Ti-imicleus concentric2is (Eaton) . Middle Bala : Onny Eiver, Shrop- 



shh'e. Impression of part of upper lamella of fringe. X 6. 

 ,, la. Ditto. Diagi-ammatic section of upper and lower lamellse, showing 



canals between opposite pits. 

 ,, lb. Ditto. Natm-al section across fringe, showing interlamellar space, 



with connecting ' pillars ' formed by union of oijposite pits, x 6. 

 ,, 2. T. hibernicus, Heed. Tramore Limestones : Tramore, co. Waterford. 



Portion of upper surface of fringe, showing pits fused and sunk 



in radial sulci, x 6. 



' Barrande, Syst. Silur. Bohenie, vol. i, pis. xxix, xxx. 

 ■•^ Eeed, Geol. Mag., Dec. V, Vol. VII, p. 212, PL XVI, 1910. 

 ^ Fearnsides, Elles, & Smith, Proc. Eoy. Irish Acad., vol. xxvi, sect. B, 

 No. 9, p. 121, pi. viii, fig. 1, 1907. 

 ^ Portlock, Geol. Rep. Londond., p. 263, pi. iB, fig. 6. 



