O’MEARA, ON DIATOMACEZ, 117 
produced and rounded ; the central space large, with an out- 
line resembling the vertebra of a fish. ‘Through this space 
there runs a well-marked median line, very fine at the out- 
ward extremity, and becoming broader towards the centre, 
at some little distance from which it terminates in a small 
bulb. The coste are arranged concentrically with the apex 
at either end for about one third the length of the frustule, 
while those in the intermediate portion spring from the 
margin of the central nodule. The central costa runs at 
right angles with the longitudinal axis, and those at either 
side radiate towards it more and more as the distance from 
this line increases. The cost in the central part of the valve 
are furcate. In some the furcation appears near the outer 
margin of the valve, in others near the central nodule; some 
few are bifurcate. It is worthy of notice that in some aspects 
the coste appear as if they were slightly notched by longi- 
tudinal lines, which, though they produce a furrow, do not 
sink so deeply as to give a moniliform character to the sculp- 
ture of the valve. 
Pinnularia constricta, n. sp., O’M., fig. 8.—Valve ellip- 
tical ; length -0044, breadth -0014; central nodule depressed ; 
coste distant, nearly reaching the median line, except at the 
central nodule ; in front view constricted, linear. 
Pinnularia forficula, n. sp., O’M., fig. 9—Valve broadly 
elliptical; length ‘0021, breadth ‘0014. In the middle is a 
blank space, curved, constricted at the central nodule, and 
towards the apices from each side converging to a point. 
The strie are distinctly costate, and longer at the middle 
than towards the apex. ‘This form in its outline closely 
resembles Navicula Smithii, var. 6, suborbicularis, described 
by Gregory in his paper on the Diatomacez of the Clyde, 
but is distinguished from it by its costate stri. 
Surirella pulcherrima, n. sp.,O0’M., fig. 10—Length ‘0046, 
breadth 0037; broadly elliptical, ends symmetrical and nearly 
lanceolate; the border narrow; the central area wide, elliptico- 
lanceolate, and striate at the margin; canaliculi about fifteen on 
each side, at first narrow, then expanding towards the outward 
margin, the narrow part short and robust ; ale conspicuous. 
Surirella gracilis, n. sp., O'M., fig. 11.—Length -0055, 
breadth ‘0037; ends symmetrical and broadly rounded ; 
canaliculi about twenty-four on either side, slightly radiate, 
narrow at first, and then expanding towards the outward 
margin, the narrow portion Jong, the expanded part first 
rounded and at a short distance from the junction slightly 
constricted, and gradually enlarging till it approaches the 
margin, where it terminates in a rounded end, separated from 
