392 F. R. Caliper Reed — The Genus Trmucleun. 



are of interest, for the lower plate of the fringe shows a narrow 

 horizontal outer baud bearing onlj- one row of pits in front, which 

 laterally by transverse division splits into two rows in regular radial 

 lines. A strong girder separates off the concave inner band, which 

 bears a corresponding number of regular radial sulci holding 2-3 pits, 

 the sulci becoming weaker or obsolete near the base of the cheeks. 

 The pits in these sulci are rather larger and fewer than we usually 

 find in T. seticornis, and this is particularly the case with the corre- 

 sponding pits on the upper plate, whicli do not lie in distinct sulci. 

 The two outer rows on the upper plate are distinct at the sides, but 

 fuse into one in front ; the radial arrangement of the lower plate is 

 preserved. This form by the reduction of the rows to one on the 

 outer band is like T. Btichlandi from Girvan, and indeed is indis- 

 tinguishable from young examples of it, but a similar type of structure 

 in the fringe has been mentioned above in specimens of T. seticornis 

 from Applethwaite, jS^orber Erow, and Cynwyd. 



Examples of T. seticornis from Portraine possess a lower plate with 

 two rows of lax'ge radial pits on the outer band, and behind the strong 

 girder there is first a separate row of isolated pits and then three 

 inner rows of smaller pits in radial sulci, both agreeing in number 

 with the outer rows. The upper plate has no definite roll, but theie 

 are twomargiiuil rows sunk in grooves with 4-5 inner rows of slightly 

 smaller pits, all arranged in regular radial lines. 



T. Bucklandi from the Sholeshook Limestone, which is doubtfully 

 separable as a species from the T. seticornis of this horizon, has the 

 0-6 rows of radially arranged small pits on the inner band of the 

 lower plate more or less fused and lying in radial sulci which are 

 more numerous than the pits of the two rows on the outer band. The 

 upper plate has the corresponding inner rows of small pits in the roll 

 lying separate and not in radial grooves. 



The better-known T. BuchlancU from Girvan ^ lias only a single row 

 of pits in front on the inferior plate outside the girder, but on each 

 side this row splits into two rows of radially arranged pit'*, as 

 Nicholson and Etheridge described.'* These pits on the upper plate 

 lie in sulci and are more or less fused, but the sulci die out on the 

 posterior portions of the fringe. The inner band on the lower plate 

 bears radial lines of small pits sunk in sulci, with a single row of 

 larger pits alternating with the radii intercalated at the base of the 

 sulci just inside the girder. A similar row is sometimes present on 

 the upper plate on which the radial rows on the roll do not lie in sulci. 



In the largest examples from Girvan attributed to this species there 

 is an abnormal develoj^ment of pits, at any rate on the iipper plate ; 

 for there are three rows of pits lying in the radial sulci near the 

 margin instead of two, and between them and the base of the roll there 

 are about three irregular rows of large, mostly alternating pits ; the roll 

 carries two or three concentric rows of more or less sunken radially 

 arranged pits of equal size, and the radii are more numerous than the 

 pits in the marginal rows. 



' Reed, Mon. Girvan Trilob. (Palasont. Soc), pt. i, p. 10, pi. i, figs. 10-14. 

 " Nicholson & Etheridge, jun., Mon. Silur. Foss. Girvan, fasc. ii, p. 193, 

 pi. xiii, fig. 19. 



