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striae among the characteristics of the genus ; his words are, 
“ moniliform, generally interrupted stiiae.” 
The present form, which occurred not unfrequently in the 
Arran material, stands distinguished from the species hitherto 
described by its plainly costate striae. 
Grunow has described a species named Grecillianum, 
“ striis transversis tenuibus,” which in this particular ap- 
proaches P. costatum, but in outline, as well as by the fact 
of having but two central vittae, is manifestly distinct from 
the present form. 
Melosira Wrightii (fig. 3), n. s. — Diameter ‘0016". The 
front view exhibits the appearance of a crown ; the sides, 
rising from the lower margin, curve slightly outwards, and 
after a little bending inwards and then downwards form a 
broad circular rim around a central depressed space, in which 
latter are two distinct nodules. The valve is perfectly 
hyaline, and without sculpture of any sort. Several forms of 
this species occurred exhibiting the side view, I considered 
them to be Melosira Westii, until I was fortunate enough 
to procure a front view, when I was convinced that they 
belong to a different species. 
Pinnularia marginata (fig. 4), n. s. — Valve elliptico- 
linear, very slightly constricted in the middle ; length 
0 0018, breadth 00008 ; striae costale, submarginal, with a 
tolerably broad span between their inner termination and the 
median line; the median space bounded by double lines, 
which spring at either side from the angles of the central 
nodule, and curving gently outwards for about half their 
length bend inwards and meet in a sharp angle at the 
terminal nodule. 
Pinnularia scutellum (fig. 5),n. s. — Valve broadly elliptical; 
length 0 0027, breadth 0 0020 ; striae costate, radiating 
towards the apices, leaving a narrow submarginal space, 
not reaching the median line ; central nodule large ; the 
median space large, lenticular, ornamented with a row of 
minute dots close to the outside of the boundary line. 
Amphiprora costata (fig. 6), n. s. — Valve elliptical, much 
constricted in the middle ; length 0 0064, breadth at widest 
part 00019, at the constriction, 00009. The keel costate; 
costae slightly radiating towards the apices, very short at 
first, gradually increasing in length for about one eighth the 
length of the entire frustule, then gradually decreasing till 
they disappear, about one eighth of the entire length of the 
valve from the central constriction. 
