F. R. Coivper Reed — Notes on Trimicleus. 355 



The species Tr. hiherniciis, Eeed,^ has the development of the stalk 

 of the glabella even more advanced than in Tr. Bticklandi or 

 2V. seticornis, the sub-spherical pseudo-frontal lobe being sharply 

 marked off from it, and the stalk itself being quite independently 

 semi-cylindrical. Traces of the first pair of lateral furrows ai'e 

 visible as weak indentations close to the axial furrows ; the second 

 and third furrows are represented by deep transverse isolated pits, 

 but the third pair has the curved extension backwards to enclose the 

 distinct basal ring. Sub-marginal pits mark the posterior ends of the 

 axial furrows, whicli are faintly traceable all the way back to them, but 

 the composite lateral lobes are indistinct, though there is the narrow, 

 elongated, depressed space on each side of the stalk occupying their place. 



Tr. alhidus, Reed,- from the Whitehouse Group (M. 13ala) of Girvan, 

 has an unusually large ovoid pseudo-frontal lobe and a well-defined 

 semi-cylindrical stalk. The lateral furrows seem to be obsolete, and 

 the composite lateral lobes and posterior part of the axial furrows 

 have disappeared ; but the fact that the meso-occipital ring extends 

 on each side of the base of the stalk shows that the structure of the 

 glabella is on the same plan. We must regard it as an extreme case 

 of suppression of segmental and primitive characters. 



We come now to a different group of species, including the 

 somewhat varied assemblage of forms called Tr. conceyitriciis, or named 

 varieties of it. In these the stalk is not developed in the glabella 

 and the lateral furrows are nearly obsolete. 



The specimens of Trinudeus from the Bala Beds of the Onny River 

 (PL XXIX, Figs. 3, 3«) usually referred to this species have an 

 elongated ovoid glabella without any differentiation into a more 

 swollen anterior, pseudo-frontal lobe and a depressed stalk ; there 

 is no sudden contraction in width, but the glabella decreases 

 gradually in height and width to its base, the axial furrows being 

 gradually convergent behind, but of uniform depth and strength. The 

 glabella at first sight appears devoid of any traces of segmentation, 

 but from the examination of a large number of specimens in different 

 states of preservation it can be confidently asserted that three pairs 

 of isolated lateral pits are present, though they are generally very 

 faint or nearly obsolete. All of them lie inside the axial furrows 

 and on the sides of the glabella. The first pair is usually obsolete ; 

 the second pair is very sliallow, transversely oval, and half-way 

 between the first and third pairs; the third pair is sometimes more 

 of a furrow than a pit, and may obscuiely mark off an incipient basal 

 ring. A fourth pair of pits lying in the meso-occipital furrow (as in 

 the seticornis group of species) is generally distinct, and lies in the 

 same axial line as the other pairs of pits, but is not connected with 

 the third furrows. Pseudo-antennary pits are always present at the 

 anterior ends of the axial furrows, and sub-marginal pits at their 

 posterior ends lying at the sides of the meso-occipital ring and outside 

 the lines of the glabellar pits. A median tubercle on the glabella 

 behind the level of the first pair of pits is present, and the meso- 

 occipital segment is furnislied with a horizontal nuchal spine. 



1 Reed, Geol. Mag., Dec. IV, Vol. II, p. 52, PL III, Figs. 2-7, 1895. 

 " Eeed, Men. Girvan Trilob., Suppl., 1914, p. 3, pi. i, figs. 1, 2. 



