210 GREVILLE, ON PLAGIOGRAMMA, 
An exquisitely beautiful object, first pomted out to me by 
my friend Professor Walker-Arnott. I have not seen the 
side view ; the specific character must consequently remain 
for the present imperfect. ‘The front view, however, is amply 
sufficient to separate it from any of the species described in 
this paper. The striz are very peculiar, broad, and appear- 
ing almost like flat plates to the eye; indeed, at first sight, 
they might be taken for costz, but they are in reality com- 
posed of two or three pieces, two only being often visible. 
Two abbreviated striae are situated between the terminal 
vittee and the angle of the frustule, the last one being a 
mere spherical granule. What importance may be attached 
to the beautiful rows of dots, analogous to those which 
occur in the connecting membrane of some Biddulphia, I 
am quite unable to say. As they are not present in any of 
the other species where I have been able to examine the 
front view, it is reasonable to conclude that they are cha- 
racteristic of the present form. It can scarcely be assumed 
that they have any connexion with the striz, as they do not 
correspond numerically. The terminal vitte in this species 
are liable to be overlooked in a hasty examination, but they 
come out quite distinctly with careful adjustment. 
7. P. inequale, n. sp., Grev.—Valve ...? terminal vitte 
in front view longer than the centrical ones, and inflected at 
the apices; length -0014” to :0016"; striz moniliform, 16 in 
001. . (Fig. 10:) 
Jamaica, in washings of alge; Nassau, New Providence, 
in scrapings of conch shells. 
It is fortunate that although, as in several of the preced- 
ing species, the side view is unknown, the front view should 
possess such well-marked features. At the first glance the 
eye is struck with the arrangement of the striz into, as it 
were, two distinct groups, caused by the centrical and terminal 
vittee being somewhat approximated, and the intervals be- 
tween them being filled up with the strie. The inflected 
apices of the terminal vitte, and the blank space between the 
centrical vittee, contribute to produce this effect. Another 
remarkable peculiarity is caused by the unequal length 
of the vittze; the terminal ones are the longest, their points 
being inflected inwards; so that the ends of the striz form 
an oblique line, descending from the points of the terminal 
to those of the centrical vitte. Then, again, the boundary 
line of the connecting membrane follows on each side the 
direction of the outline formed by the ends of the striz, and 
the result is more or less of a rhomboidal figure, of little 
