F. R. Con-per Eeed — The Genus Trinucleus. 391 



outer rows of pits on the lower plate, which are sepai'ate and radially 

 arranged at the sides, approach one another iu front and fuse into one 

 row, so that the girder has here only a single row of pits outside it. 

 The pits on the inner concave band are arranged in three or more 

 rows and in radial lines equal in number to the pits on the outer band, 

 but do not lie in sulci. 



In specimens from jSTorber Brow the two outer rows on the outer 

 band fuse into one as in the Applethwaite form, but the pits of the 

 third row (i.e. the first one inside the girder) become larger in front, 

 and the radial lines of 3-4 pits slope inwards to the median axial 

 line on each side. 



In a specimen in the Jermyn Street Museum from Cynwyd, 

 Merioneth, there is a similar reduction to a single row on the outer 

 band in front, but on the concave inner band the 3-5 rows of small 

 pits lie in sulci in front and half round the sides, while the sulci 

 become obsolete further back. Just inside the girder at the sides of 

 the cheeks at the base of these radial sulci there is intercalated 

 a single detached row of larger pits in the same radii as those on the 

 outer band. 



Examples from Pusgill Beck show two regular continuous rows of 

 pits radially arranged, but not in sulci, on the outer band, and in the 

 same radii on the inner band lie 3-4 rows of smaller pits in shallow 

 sulci extending round nearly to the base of the cheeks. On the upper 

 plate the reverse is found, the inner rows having the pits lying 

 isolated and not in grooves, while there are radial grooves in the outer 

 part of the fringe each, holding three pits, the outermost pit being 

 additional, smaller, and not represented on the lower plate. 



In the numerous specimens from the Redhill Stage of the Haverford- 

 .west area the two rows on the outer band of the lower plate have the 

 pits radially arranged and distinct, and not in grooves ; the pits of the 

 outer row are apt to be rather larger than those of the second row. 

 On the inner concave band there are radial sulci agreeing in number 

 with the pits on the outer band and holding 2-3 small pits. On the 

 upper plate there are two outer rows of pits Ij^ing in short radial sulci, 

 and inside them on the roll are rows of small pits radially arranged 

 and corresponding to those on the lower plate but not placed in sulci. 

 In some cases these inner radial lines of small pits are more numerous 

 than the pits in the outer grooves. 



The specimens from the Sholeshook Limestone agree with those 

 from the Redhill Stage in the characters of the lower plate, except 

 that the pits of the two rows on the outer band are equal in size, 

 and on the inner band the radial sulci (which usually hold 3-4 pits) 

 die out near the genal angles. In some individuals, however, we 

 notice that the pits on the outer band lie in radial grooves and are 

 more or less fused. An intermediate condition is found in specimens 

 from the Slade Beds, for in them it is only the pits in the median 

 front portion of the outer band which tend to lie in grooves, those at 

 the sides being isolated (PI. XIX, Figs. 5, 5a). 



The specimens from Tyrone attributed to T. seticornis by B. Smith ^ 



' Fearnsides, Elles, & Smith, op. cit. , p. 122, pi. viii, figs. 7, 8. 



