90 WALKER-ARNOTT, ON RHABDONEMA. 
Annuli numerous, about 11 in ‘001, with about 15 cells in 
‘001. Septa apparently wanting, but from the external ap- 
pearance of the frustule, they seem to exist, although in a 
very rudimentary state, and to be alternate; they have con- 
sequently no perforations. Valves the breadth of the annuli, 
flat, usually more or less ovate and acuminate, sometimes 
linear-oblong. Strize only between the costz, oblique, about 
30 in ‘001, easily seen with a quarter-inch object-glass. 
2. Eu. ocellata; annuli as broad as the nearly flat valves, 
finely striate ; the septa contiguous to the valves, perforate. 
Hab. New Zealand, on Ballia callitricha. 
Annuli numerous, about 13 in ‘001, with about 40 striz 
in ‘001. Septa opposite, those nearest the valves composed of 
coste similar to what are seen on the valves, but with the 
interstices open ; the rays on the front view (formed by the 
subjacent septa) diverging from the lower valve, and con- 
verging from the upper one, indicate that these openings 
enlarge, while the septa themselves become narrower and 
fainter as they approach the middle of the frustule, where 
they are evanescent or rudimentary. All the annuli do not 
project the septa simultaneously ; those next the valves do so 
first, the last projected being the most remote: a frustule, 
therefore, may present itself which has only the annulus 
next the valve provided with septa, and one solitary example 
occurred where even then they had not been formed or were 
wanting; when this takes place, the species can scarcely be 
distinguished from the followmg one, except by the flatness 
of the valve, the coarser striz on the annuli, and the breadth 
of the annuli as compared with the valve. Valves nearly flat, 
not perceptibly broader than the annuli, elliptic linear or 
sometimes slightly lunate, rounded at each extremity. The 
striz are so faint that I have not been able to observe 
them satisfactorily. 
Mixed with this, and parasitical along with it, are seve- 
ral frustules of what at first sight resembles a minute 
Himantidium ; but 1 have not yet ascertained its side view, 
and as its genus is as yet doubtful, it is unnecessary to allude 
to it further. 
3. Eu. incurvata ; annuli conspicuously narrower than the 
very convex valves, delicately striate ; septa entire. 
Hab. West coast of Africa (among guano from Ichaboe, 
1855).* 
* T would not have introduced this species had I not seen many front as 
well as side views of it, as it is seldom that any certain conclusion can be 
obtained from deposits, dredgings, or guanoes. As an instance of a mis- 
take occurring in that way, I may allude to Pleurosigma compactum, Grev., 
