226 TRANSACTIONS OF THE [May 18, 
tubercles, only visible with a lens. Size of this caudal shield, 
length and breadth each 9 mm. 
Horizon and Locality. Grey shales of the P. Davidis Zone at 
Manuel Brook, Conception Bay, Newfoundland. 
This species is distinguished from A. scarabeoides, Hicks, by 
the absence of visible tubercles on the surface of the test. 
AGNOSTUS GIBBUS, Linnarsson. 
Agnostus gibbus, Linrs. Om Vestergot. Cambr. Silur. Aflagr. 
p. 81, tab. ii., figs. 52, 53. 
Agnostus gibbus, Broegg. Om Paradox, lagr. v. Krekling, tab. 
Vin, fe. a 
Agnostus gibbus, Linrs. Om faun. i Kalk.m. Conocoryphe ex- 
sulens, p. 22, tafl. ii. figs. 31,32. 
Agnostus gibbus, Tullb. Om Agnostus-arterna, p. 15, tafl. i., 
fig. 2,a and b. : 
The following is the diagnosis of this species: ‘ Test smooth. 
Head surrounded by a narrow subfiliform border. Glabella 2- 
lobed, anterior lobe rounded-subtriangular, equalling the poste- 
rior lobe in width, posterior lobe elevated into a tubercle, often 
very tumid, in the anterior part of which tubercle an elevated 
point can sometimes be seen. Basal lobes small, entire, rounded 
triangular, connecting behind the above tubercle by a narrow 
rim. Cheeks without lateral grooves, separated in front of the 
glabella by an impressed line. Pygidium rounded, without 
spines, and having a narrow border fold. Rachis 3-jointed, the 
anterior joint divided. into three parts by two longitudinal de- 
pressions, of which the middle is the smallest ; the middle joint 
narrower than the others, but much higher, produced backward 
into a rather long, free denticle which almost always is broken off; 
the posterior lobe large, convex, rounded-acuminate behind, Lat- 
eral lobes narrowed behind, separated by an impressed line.” 
Horizon and Locality.—Grey shale of Div. 1c¢.1. St. John, 
N.B. Canada. Scarce. 
Size.—Length and width of the shields, 5 mm. 
Tullberg says the name is derived from the projecting spine 
on the rachis of pygidium, “directed backward and upward” 
[but the back of the glabella is said to be very tumid (“ tumi- 
dissimum”’) ]. 
The varieties and forms included under this species by Swedish 
geologists allow one to consider it a flexible species, liable to 
considerable change of form. It is thus capable of including 
two forms which we have described in the Transactions of the 
Royal Society of Canada as separate species; there is the more 
