O’MEARA, ON DIATOMACE. 115 
the centre. Puncta or granules larger towards the centre than 
at the margin.” In the other form the rays are distinctly 
marked through the entire length, some of them reaching the 
centre, others terminating at some distance from it, and others 
extending but a short distance from the margin. The granules 
forming the rays are considerably smaller than those of the 
other species referred to, and the central ones are scarcely 
larger than those at the margin. 
For these reasons I consider the two forms should be re- 
garded as distinct species, and suggest that henceforth the name 
Coscinodiscus Gregorianus should be given to the form found 
by Dr. Gregory in the Glenshira Sand. 
I now proceed to mention a fact deserving of special atten- 
tion, namely, this—that Tessella Interrupta, Eupleuria Pul- 
chella, and forms belonging to the genera Hyalodiscus and 
Omphalopelta, have been met with in this collection. These 
species have been discovered in distant parts of the world, 
but, so far as I can learn, have not hitherto found a place in 
the list of British diatoms. 
But the number of forms which, so far as I have been able 
to ascertain from the sources of information available to me, 
have not been hitherto described, constitutes the most inte- 
resting feature of this valuable collection. Some of these I 
shall hold over for further examination, and now submit to 
your consideration a few of these new forms, with their 
descriptive characters. 
Navicula Hibernica, n. sp., O’M., Pl. V, fig. 1.—Broadly 
elliptical; length ‘0041, breadth -0024; striz very fine, con- 
fined to a narrow marginal band ; parallel to the median line 
there is a broad band without striz, linear, interrupted at the 
central nodule, constricted towards the ends, and rounded; 
the central portion of the valve is granulated. ‘This pretty 
form is closely allied to Navicula indica, Grev., but has not 
the mammiform apices nor the lyrate blank space of that 
beautiful species. 
Navicula pellucida, n. sp., O’M., fig. 2.—Length -0036, 
breadth ‘0013; constricted; striz very fine, confined to a 
very narrow marginal band, shorter towards the ends and 
the central constriction ; the inner part of the valve smooth, 
pellucid; at either side of the median line divided into two 
compartments by a longitudinal curved line; in front view 
constricted, marked at the centre and ends by bead-like 
nodules. 
Navicula denticulata, n. sp., O’M., fig. 3—Length of 
valve ‘0034, breadth ‘0013; deeply constricted; striz costate 
rather than moniliform, marginal, with a narrow, striate, 
