122 TRANSACTIONS OF THE [maR. 17, 
Horizon and locality. Sandy layers of Assise 2 in Band 3, at 
Hanford Brook. Scarce. 
A description of the Protolenus Fauna would be incomplete 
without an account of one remarkable species, which is so con- 
stituted that it to some extent bridges the gulf between the two 
great orders of Brachiopods, the Articulata and Inarticulata ; 
or rather it should be said that this form, which must be classed 
in the latter order, had a mechanical contrivence for hinging the 
valve similar to that possessed by the Articulata;* an order of 
which only rare individuals have been found in the Protolenus 
Fauna, and which is but poorly represented in the Fauna of 
Olenellus, but which became so vastly expanded in later ages. 
TREMATOBOLUS.+ 
TREMATOBOLUS INSIGNIS, Matt., Pl. iv., figs. 2 a—d. 
Trematobolus insignis, Matt., Can. Rec. Sci., Jan., 1893, p. 276, 
figs. 1 a—d. 
Trans. Roy. Soc. Can., vol. xi., sec. iv., p. 88., pl. xvi., figs. 4 
a tod. 
Shell a meniscus, inequivalve, articulate. Valves thin, closely 
applied. Shell substance caleareocorneous ? 
Dorsal valve oblately circular, concave. At the hinge is a 
long, narrow socket, at right angles to the plane of the valve, 
fitted to receive the anterior edge of the ventral valve. The 
socket is interrupted in the middle by a cardinal process; this 
process extends into the interior of the valve, and is flanked on 
each side by a small, deep pit. At the back of the shell, on 
each side of the cardinal process, is a dental plate, and in front 
of it two transverse, lobed, triangular depressions, supposed to 
be due to the posterior adductor (cardinal) muscles. On each 
side of the shell, adjoining these depressions, are the scars of 
the adjustor muscles. There is a broad, shallow groove along 
the median line of the valve which would mark the part of the 
shell’s interior traversed by the adductor muscles during the 
growth of the shell; this depression is divided lengthwise by a 
low ridge, and forks at the middle of the valve into two arched 
branches, which include between them a shorter depression. 
There are several faint, raised vascular lines (about four on 
each side of the median line of the valve); of these lines the 
*Mr. Chas. Schuchert writes to me to say that he includes this form in Beacher’s 
order Neotremata. 
+Can. Rec. Sci., Jan., 1893, p. 276. 
