42 
Dr. Gregory, on the Post-tertiary 
N. quadrata^ and N. granulata, are marine forms, and that 
they all occur in recent gatherings on our coasts. 
6. Navicula formosa, n. sp. This is a very beautiful form, 
and is frequent in the coarser densities of the deposit. 
Form, an elegant linear elliptic, or elliptic lanceolate, with 
somewhat obtuse extremities. Nodules large and definite ; 
median line like that of many Pinnularice^ such as P. viridis. 
Stri2e slightly inclined, about 35 in '001", not reaching the 
median line. There is, on each side of the median line, a 
side line, parallel to it. Length from O'OOS" to 0*0065." At 
one time I referred N. maxima ^ and this form to one species, 
but in ]V. formosa the striae, besides being inclined, and not 
reaching the median line, are much more conspicuous, giving 
to the form a peculiar and well-marked aspect. I had also 
some doubts, whether it should not be referred to Pinmilaria^ 
rather than Navicula^ but I have preferred the latter, because I 
believe the striae to be moniliform, though very minutely so. 
Fig. 6 represents a specimen, nearly of the average size ; it 
is, however, often considerably longer. I have not yet seen it 
elsewhere. (264.) 
7. Navicula pulchra, n. sp. This very pretty form is not so 
frequent in the deposit as most of the preceding species. 
Form, elliptic lanceolate, almost rhombic, with a slight in- 
flexion towards the extremities ; not very broad. Length about 
0'003." Striae not very fine, very highly radiate, and very 
strongly moniliform, which gives to it a very peculiar aspect. 
Fig. 7 represents what appears to be the typical form, which 
I have only seen in this deposit. (265.) 
8. Navicula angulosa, n. sp. This very beautiful form is 
frequent in the medium densities of the sand. 
Form elliptic lanceolate, rather broad, with acute apices. 
Length from 0-0025" to 0 0045." Striae conspicuous, marginal, 
and bounded, internally, by an angular, rhombic space. No- 
dules definite, median line sharp and distinct. It is repre- 
sented of the average size in fig. 8. I understand from Mr. 
Bleakley, that he has found this form on our eastern coasts. 
Var. /3. Rather smaller. Form linear, sides parallel, ends 
acuminate, striae more distant ; otherwise agreeing with a. 
Represented in fig. 8*. This also seems to have occurred to 
Mr. Bleakley. 
Perhaps this species ought to be referred to the genus 
Pinnularia, but it is not easy to define these two genera. We 
shall see presently that moniliform or costate striae are not 
always to be depended on, although Professor Smith distin- 
guishes them by these characters. I was at one time persuaded 
to refer this form to N. palpehralis, but having carefully 
studied authentic specimens of that species, I am satisfied that 
