F. R. Coivper Reed — Notes on Trinucleus. 357 



and of a basal annular swelling are points of resemblance in the 

 glabella, but the furrows and lobation are quite diiferent. 



The Bohemian species Tr. Goldfiissi, Barr.,* of which I have 

 examined nearly a dozen examples of the head-shield, appears to 

 furnish an explanation of the two pairs of small but deep and well- 

 marked pits at the base of tlie glabella, which I have described above in 

 Tr. gibhifrons. For in Tr. Goldfussi there are, in addition to these small 

 deep pits, three pairs of very shallow isolated pits of larger size and 

 set at equal distances apart on the flanks of the glabella, as in the 

 Onny Biver specimens of Tr. concentricus. These pits are only rarely 

 visible, but where present the third pair is continued back by very 

 weak furrows to the small deep pits in the axial furrows, thus showing 

 that these pits may be regarded as marking the outer ends of the third 

 lateral furrows. Behind them come the similar small deep pits in 

 the meso-occipital furrow, as in Tr. gibhifrons. These two pairs of 

 small pits are shown in Barrande's figures of Tr. Goldfussi and seem 

 to be generally developed in all its allies. 



In Tr. NicJiolsoni, Beed,'' the glabella has the elongated ovoid shape 

 of Tr. concentricus (Onny Biver form), narrowing gradually behind, 

 but the anterior part is more swollen and there is a median tubercle 

 as in Tr. gibhifrons. The axial furrows are very deep and converge 

 regularly behind without any contraction ; the first and second 

 furrows are very shallow faint depressions in the axial furrows, 

 indenting the base of the sides ; the third and fourth pairs of pits are 

 sharp and deep, like those in Tr. gibhifrons, and there is likewise 

 a weak basal annular swelling with low lateral nodules. A nuchal 

 spine is present as in Tr. concentricus. Undoubtedly this species is 

 closely connected with the latter. 



With regard to the distinct species or varieties of Tr. concentricus 

 described by Portlock from Tyrone, we can only speak with certainty 

 of the form known as Tr. coficentricus, var. elongatus,^ so far as the 

 characters and lobation of the glabella are concerned. This form has 

 a long sub-pyriform glabella much like that of the Onny Biver 

 Tr. coticentricus in general shape ; the pseudo-antennary pits are 

 distinct ; there are no traces of any first or second pairs of furrows or 

 pits; two pairs of small deep, rather closely placed pits at the base 

 of the glabella represent the third and fourth pits, the anterior pair 

 of which lie in the axial furrows, the posterior pair rather further 

 inwards and in the meso-occipital furrow. Both pairs are deep and 

 subcircular. Sub-marginal pits are also present, and the meso-occipital 

 ring bears a sharp median tubercle. 



The Girvan species Tr. subradiatus, Beed,* from the Balclatchie 

 Beds, possesses a glabella which in its general shape (apart from its 

 carination) resembles that of Tr. coticentricus of the Onn)' Biver, and 

 the meso-occipital ring has likewise a horizontal nuchal spine. The 



^ Barrande, Syst. Silur. Boheme, i, p. 628, pi. xxx, figs. 29-40 ; pi. xxxv, 

 figs. 30, 31. 

 - Keed, Geol. Mag., Dec. V, Vol. VII, p. 212, PI. XVI, Figs. 1-9, 1910. 



* Portlock, Geol. Kep. Londond., p. 263, pi. iB, fig. 7; B. Smith, Proc. 

 Roy. Irish Acad., xxvi, B, 9, p. 127, pi. viii, figs. 3, 4, 1907. 



* Reed, Girvan Trilobites, 1903, pt. i, p. 12, pi. ii, figs. 1-6. 



