6 BRITISH CAMBRIAN TRILOBITES. 



Types. — The originals of Hicks's ^i. scarab&oides and A. scutalis, figs. 9 and 10, 

 are in the Sedgwick Museum, Cambridge. 



Horizon and Localities. — Menevian : Porth-y-rhaw, St. David's ; Dolgelly. 



o. Agnostus davidis, Salter. Plate I, fig. 7. 



1866. Agnostus davidis, Salter, Brit. Assoc. Rep. for 1865, p. 285. 



1872. Agnostus davidis, Hicks, Quart. Journ. Geol. Soc, vol. xxviii, p. 174, pi. v, figs. 2 and 4 (fig. 3 



is doubtful). 

 1896. Agnostus davidis, Matthew, Trans. N. Y. Acad. Sci., vol. xv, p. 225, pi. xvi, fig. 6. 



Head semicircular, with narrow margin. Glabella large, bilobed ; anterior lobe 

 large, semicircular ; posterior lobe widens posteriorly, and is raised anteriorly into 

 a large quadrate eminence constricted in the middle ; basal lobes large, elongated, 

 triangular. The cheeks are wide posteriorly and contract forwards, and are 

 separated in front of the glabella by a faintly impressed line; surface rugose. 



Thorax : axis broad, consisting of three raised portions, nearly equal in size ; 

 pleurae grooved, the groove in the first segment being near the posterior margin. 



Tail nearly semicircular, with a fairly wide flat margin. Axis broad, showing 

 the segmentation very imperfectly, but it appears to have been divided into three 

 segments, the first wide but very short, the second probably hexagonal and slightly 

 keeled, while the last is broken. Lateral lobes rugose. Margin widens posteriorly. 



Head- and tail-shields 6 — 7 mm. long, 9 — 10 mm. wide. 



This form is still very imperfectly known, and most of the specimens which 

 have been referred to it in our museums belong to other species, including such 

 diverse forms as A. barrandei and A. fissus. The most peculiar feature of Hicks's 

 figured types (figs. 2 and -1) is undoubtedly the extraordinary elevation in the 

 front portion of the posterior lobe of the glabella. The very large size of the 

 species is remarkable, but the imperfect preservation of the types and the fact 

 that no better specimens have yet been found which can be referred with certainty 

 to the same species, unfortunately prevent me from instituting any satisfactory 

 comparison with other forms. The characters of the tail in particular must still 

 remain in doubt. 



Types. — The originals of Hicks's figures 2 and 4 are in the Sedgwick Museum, 

 Cambridge. 



Horizon and Locality. — Menevian : Porth-y-rhaw, St. David's. 



4. Agnostus exaratus, Gronwall. Plate I, figs. 8 — 10. 



1866. Agnostus scutalis, Salter (pars), Brit. Assoc. Rep. for 1865, p. 285. 



1872. Agnostus scutalis, Salter (pars), Hicl<s, Quart. Journ. Geol. Soc, vol. xxviii, p. 175, pi. v, figs. 



12 and 13, and probably figs. 11 and 14 ; not figs. 9 and 10. 

 1902. Agnostus exaratus, G-ronwaU, Bornholms Paradoxideslag, p. 77, pi. i, fig. 17. 



