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



glaljella is swollen at its base and has a decided sub-nodular elevation 

 at each side between the oblique third furrows and the meso-occipital 

 stalk. The fourth pair of pits are large and deep. The sub-marginal 

 pits at the posterior ends of the feebly impressed axial furrows are 

 smaller than the others and lie outside the longitudinal lines in which 

 they are arranged, as in Tr. seticornis. Though the axial furrows are 

 indistinctly marked behind the pseudo-frontal lobe, and a wide 

 depressed area on each side of the stalk of the glabella separates the 

 latter from the cheeks, yet they can be traced with care the whole 

 way back from the pseudo-antennary pits to the sub-marginal pits, 

 and indicate the true ovoid shape of the entire glabella. 



In the larger specimens of Tr. Bucklandi from Girvan (PI. XXIX, 

 Fig. 2), usually considered as the adult form of those above described, 

 the first pair of lateral furrows is better marked, and the second and 

 third pairs nearly meet at their inner ends ; the lateral composite lobe 

 is more differentiated and swollen along the axial furrows, and there 

 is a small outer extra pit lying in or nearly in the axial furrows 

 between the third and fourth pairs, as in Tr. fimlriattis. The formation 

 of the basal ring, and the size and development of the fourth pits, the 

 pseudo-antennary pits, and sub-marginal pits are as in the smaller 

 form. Nicholson & Etheridge ^ noticed the first pair of lateral 

 furrows in this species, and they were faintly shown in some of my 

 figures of the species,^ but their character and homology were not 

 discussed. The general ovoid outline of the glabella is well seen in 

 these specimens, the axial furrows being distinctly visible on each 

 side, curving gently in with a slight convergence to the base of the 

 glabella. In this form we may specially notice the strength of the 

 lateral furrows, their approximate entry into the axial furrows, 

 and the consequent tendency for the elongate composite lateral 

 lobe to be resolved into its several pairs of lobes, the second 

 pair of lateral lobes (between the second and third pairs of furrows) 

 being nearly quite marked olf and circumscribed. McCoy ' in 

 describing this species seems to have observed second, third, and 

 fourth pairs of pits or furrows, for he says "the posterior half of the 

 glabella [is] abruptly contracted to a narrow neck with a distinct 

 neck-furrow [= meso-occipital furrow] and two short segmental 

 furrows at each side [= second and third lateral furrows], the ends 

 forming three deep punctures in casts". It may be mentioned here 

 that the median tubercle on the pseudo-frontal lobe, which is so 

 conspicuous in the smaller form, is much reduced and sometimes 

 wanting in these larger specimens of Tr. Bucklandi. 



Without attempting to discuss the form from Scania referi'ed by 

 Olin* to Tr. Bucklandi^ it may be remarked that his figures indicate 

 clearly that the glabella has an ovoid shape and includes lateral 

 composite lobes scarcely differentiated from a median stalk, with well- 

 developed true axial furrows. 



^ Nicholson & Etheridge, op. cit., p. 192. 

 " Eeed, op. cit., pi. i, figs. 10, 13. 

 ^ McCoy, Syn. Pal. Foss. Woodw. Mus., p. 147. 



* Olin, " Chasmopsk. o. Trinucleusskiffern i Skane " : Medd. fr. Lunds 

 Geol. Faltklubb, ser. B, Nr. i, 1906, p. 66, t. iv, figs, la, h. 



