8 BRITISH CAMBRIAN TRILOBITES. 



Types. — The original of Hicks's fig. 12 is in the Sedgwick Museum, Cam- 

 bridge (also the originals of his figs. 9 and 10, which do not belong to this species). 



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

 St. David's. 



5. Agnostus reticulatus, Angelin. Plate I, fig. 11. 



1852. Agnostus reticulatus, Angelin, Pal. Scand., p. 8, pi. vi, fig. 10. 



1867. Agnostus nodosus, Belt, G-eol. Mag., vol. iv, p. 295, pi. xii, fig. 3 a and b. 



1880. Agnostus reticulatus, Tullberg, Agnostus-arterna, p. 23, pi. i, fig. 12 a, b. 



1882. Agnostus reticulatus, Brogger, Die Silur. Etagen 2 und 3, p. 57, pi. i, fig. 11 a, b. 



Head semi-elliptical, with narrow margin. Glabella narrow, bilobed ; anterior 

 lobe subquadrate, not very definitely marked off from the posterior lobe behind, 

 nor always from the cheeks ; frequently cleft in front by a deep furrow which 

 extends forwards into the cheeks ; posterior lobe elongate, raised into a prominent 

 tubercle about the middle ; basal lobes small, triangular. Cheeks wide, nearly 

 uniform in width, marked by numerous reticulate furrows which show a tendency 

 to a radial arrangement. 



Tail semi-elliptical, with narrow margin, which bears a minute spine on each 

 side. Axis long, narrow, divided into three segments ; the first segment is short 

 and divided into three nodules ; the second is somewhat larger and is formed of 

 a large central lobe, and two lateral lobes on each side ; the third segment is long 

 and pointed, and divided longitudinally into three portions ; the central portion 

 is divided transversely into a large anterior lobe, and a smaller posterior lobe ; the 

 lateral portions are each divided into a number (six according to Tullberg) of 

 small tubercles. The lateral lobes are wide and marked with reticulate furrows. 



Head- and tail-shields 3*5 — 5*5 mm. long and wide. 



Among the British species the only form with which A. reticulatus is likely to 

 be confused is A. trisectus, which resembles it closely in the ornamentation of the 

 cheeks, so that although the two species are very distinct, yet when badly pre- 

 served they may be confounded with one another. The comparatively narrow 

 glabella of A. reticulatus, its indistinct basal lobes, and somewhat ill-defined anterior 

 lobe will, however, usually suffice to distinguish it; while in the tail the narrow and 

 pointed axis will generally be visible even in imperfect specimens. 



The British forms seem to be almost, if not quite, identical with those described 

 by Tullberg from Scania. Tullberg, however, does not refer to the cleft in the 

 anterior lobe of the glabella, and figures that lobe as much more distinctly defined 

 than in our specimens. So far as the tail goes, there seems to be no difference, 

 except that our specimens are seldom perfect enough to show the subdivisions of 

 the axis, and sometimes only the central portion of the axis is at all distinct. 



