ere Val 2 ee 

182 Cincinnati Society of Natural LFiistory. 
gently curving into the ends. Ventral overlap distinct. Surface 
smooth and even, without eye tubercle or muscle spot. 
The development of a flange at the dorsal border ig a very 
unusual feature in this genus. JZ. simwata, Hall, has nearly the 
same shape, but is without a flange, and, so far as known, its 
valves do not overlap at the ventral margin. I am inclined to 
believe that species of this character ought to be arranged with 
Aparchites rather than Leperditia. 
Position and locality: Devonian Bryozoa bed, Falls of the 
Ohio. Rare. 
ISOCHILINA RECTANGULARIS, Nn. Sp. 
Flate XVI, Figs. 2 a, b, ¢. 
Size of left valve: Length, 1.22 mm.; height, o.81 mm.; thick- 
ness, 0.21 mm. | 
Carapace small, nearly symmetrical, with the straight hinge-line 
nearly as long as the valves, the upper fourth of the anterior edge 
a little oblique; below this the free margins to the posterior 
cardinal angle form a semi-circle. Upper half of posterior margin 
forming nearly a right angle with the hinge-line. This feature 
has suggested the name. A well-defined though rather narrow 
flange encircles the entire valve. Valves moderately convex, with 
point of greatest convexity in the posterior half. Eye tubercle 
not developed. 
There are several species of Leperditia known that resemble this, 
but as ours is clearly an Jsochilina, as that genus is now under- 
stood, there is little likelihood of confusion between them. I know 
of no Devonian species with which it could be confounded. 
Position and locality: Same as the preceding. 
APARCHITES INORNATUS, Nn. Sp. 
Plate XVI, Pigs. 31a. 3x0. 
Size. of left valve: Length, 0.8°mm.; height,o.5)ammiemiariGk- 
ness, 0.2 mm. 
This species is closely related to the Silurian A. wazcornis (Leper 
ditia untcornis, Ulrich). Prof. Jones .places that species with 
FPrimitia, while to me Afarchites appears as the genus that should 
receive it and other forms of like character. In the present species 
