356 F. R. Cowper Reed — Notes on Trinucleiis. 



In Tr.favus, Salter,^ the glabella (PI. XXIX, Fig. 4) has the same 

 shape and characters as these Onny specimens of Tr. concentricus ; 

 three pairs of small shallow isolated pits can be more easily detected 

 on the lateral slopes of the glabella, all unconnected with the axial 

 furrows, the first ones being as much isolated as the others, but all are 

 equidistant and sub-equally developed. A small fourth pair of pits 

 in the meso-occipital furrow is also visible and pseudo-antennary 

 pits at the anterior ends of the axial fuiTOws. There is a median 

 tubercle also on the glabella. Practically the segmentation and 

 pitting is the same as in Tr. concentricus of the Onny River. 

 Tr. favus is typically a Llandeilo form. 



There is a form of Trinucleus, usually referred now to Tr. con- 

 centricus, which was separated by McCoy ^ as a distinct species which 

 he called Tr. gihhifrons (PI. XXIX, Figs. 5-7). The tj'pe-specimen 

 of it cannot be found, but there are several specimens in the Sedgwick 

 Museum from the Bala Beds of AUt yr Anker, Dinas Mawddy, and 

 Pen y Craig, which were labelled by McCoy as Tr. gihhifrons and 

 possess the characters which he described. In this form the glabella 

 is shorter, broader, and more inflated than in the Onny River 

 Tr. concentricus ; the anterior part of the glabella is somewhat 

 independently swollen into an incipient pseudo-frontal lobe ; the 

 posterior and shorter part of the glabella is slightly contracted at 

 the base of this lobe and rather suddenly depressed, suggesting the 

 formation of a stalk. The first pair of lateral pits is very weak and 

 often scarcely discernible, indenting the sides of the anterior swollen 

 portion ; the second pair is likewise very faint or obsolete. There are 

 then two much more distinct small sharply marked deep pits on each 

 side of the base of the glabella ; the anterior of these pits lies almost 

 in the axial furrows and probably corresponds with the third pair in 

 Tr. concentricus and others, but must represent the outer instead of the 

 inner ends of these fuirows (see remarks on Tr. Goldfussi below) ; 

 between this pair a slight annular basal swelling of the glabella is 

 noticeable, suggesting the basal ring of Tr. Bucldandi, etc. The 

 posterior pair of pits apparently correspond with the fourth pair in 

 the meso-occipital furrow, and are rather more inwardly situated than 

 the third pair. The pseudo-antennary pits at the front ends of the 

 axial furrows and the sub-marginal pits at their posterior ends are 

 well marked. The axial furrows themselves are wider and less 

 deeply impressed towards the base of the glabella, but there are no 

 composite lateral lobes and the axial furrows plainly bound the 

 glabella for its whole length and width. There is no horizontal 

 nuchal spine to the meso-occipital ring, but a strong pointed 

 median tubercle or short vertical spine is present on this ring. 

 A median tubercle also is present on the swollen anterior part of 

 the glabella. 



We may regard this form, Tr. gihhifrons, as belonging to a parallel 

 line of development to Tr. seticornis and its allies, but not directly 

 connected with it. The inception of a pseudo-frontal lobe and stalk 



' Salter, Mem. Gaol. Surv., vol. ii, pt. i, p. 350, pi. ix, fig. 3 ; vol. iii, 

 p. 517, pi. xiii, fig. 9 ; dec. vii, pi. vii, p. 6. 



2 McCoy, Syn. Pal. Foss. Woodw. Mus., p. 145, pi. iE, figs. 14, 14a. 



