358 F. R. Goivioer Reed — Notes on Trinucleus. 



first two pairs of lateral furrows of the glabella, tlioiig;li very short 

 and often mere notches indenting the sides of the glabella, start from 

 the axial furrows; the third pair is longer and oblique, the outer 

 end of each furrow being marked by a deep pit set far back in the 

 axial furrow. There is a fourth pair of pits transversely oval in 

 shape and set rather further inwards in the meso-occipital furrow ; 

 and sub-marginal and pseudo-antennary pits are likewise present. 

 Traces of a faint basal ring are generally visible. 



Several British species are not sufficiently known to enable us to 

 discuss adequately their glabellar segmentation. Such are Tr. latun, 

 Portl., Tr. radiatus, Murch., Tr. Thersites, Salter, and Tr. Lloydi, 

 Murch. 



In the case of Tr. radiatus, Murch. ,^ the second and third lateral 

 furrows seem represented by two deep triangular pits, of which the 

 anterior pair is situated behind the middle of the glabella, and the 

 third pair has a slight connecting groove across the base of the glabella, 

 marking ofl a basal ring. 



Salter's^ figures of Tr. Lloydi show a feebly marked, narrow, 

 elongated, lateral composite lobe on each side of the posterior half of 

 the glabella, and in Fig. 1* a decided basal ring, but he only 

 mentions "a slight longitudinal depression on each side " (marking 

 off the lateral lobe) and " one obscure lateral sulcus above the neck- 

 furrow " at its base ( = the third lateral furrow). The condition of 

 the lateral composite lobes recalls that found in Ampyx nudus, Murch. 



Tr. Thersites, Salter,^'shows no stalk and no furrows on its narrow 

 compressed carinate glabella ; this species has never been figured, and 

 the type-specimens are hardly sufficient for an adequate specific 

 diagnosis. 



EXPLANATION OF PLATES. 

 Plate XXVIII. 

 Fig. 1. Trinucleus fimbriatus, Murchison. x 3. Llandeilo Beds : Pen 

 Cerrig, Builth. 



,, 2. Ditto. X 2. Same horizon and locality. 



,, 3. Ditto. X 3. Same horizon and locality. McCoy's figured specimen, 

 Syn. Brit. Pal. Foss. Woodw. Mus., pi. lE, fig. 16. 



, , 4. Trinucleus Mtirchisoni, Salter. X 2 J. Arenig Series : Tasker Quarry, 

 near Shelve. 



,, 4a. Ditto. X 2|. Impression of same specimen. 



,, 5. Trhiucleus seticornis, Hisinger. x 2 J. Sholeshook Limestone: 

 Sholeshook, Pemb. 



,, 5a. Ditto. X 2|. Side view of same specimen. 



,, 6. Trinucleus Buchlandi, Barrande (small form). X 2^. Drummuck 

 Group : Thraive Glen, Girvan. Mrs. Gray's Collection. 



,, 6a. Ditto. X 2 J. Side view of same specimen. 



Plate XXIX. 

 Fig. 1. Trinucleus Buchlandi, Barrande (small form). X 2J (with one 

 thoracic ring attached). Drummuck Group : Thraive Glen, Girvan. 

 Mrs. Gray's Collection. 

 ,, 2. Ditto (large form). X IJ. Same horizon and locality. Mrs. Gray's 

 Collection. 



^ Murchison, Silur. Syst., pi. xxiv, fig. 3. 



^ Salter, Mem. Geol. Surv., dec. vii, pi. vii, 1853 (the figures are largely 

 restorations). 

 ^ Ibid., p. 7. 



