GREVILLE, ON NEW DIATOMS. 235 
puncta quite obscure, while in the produced angles beneath 
the capitate extremity there are a few large puncta. On 
the other hand, iv our present species radiating puncta 
occupy the whole valve; there is also a row of marginal 
puncta not to be seen in the other ; the produced angles are 
narrower, and the apex much less rounded. With regard to 
the spines, I have seen sometimes two, sometimes three 
(doubtless the normal number), and sometimes have been 
unable to detect them at all. Whether in the latter case 
they had been broken off and left no trace, or whether they 
are occasionally undeveloped, I am unable to say. 
Enrocontia, nov. gen., Grev. 
Frustules with the lateral view triangular, containing a 
central triangular figure, having a broad border divided by 
transverse coste into punctate or cellulate compartments. 
I propose this genus for the section of Triceratium of 
which for some time 7. marginatum of Brightwell was the 
only representative. In my Series IV, (Trans. Mic. Soc.,’ 
vol. ix) I added six additional species, and in Series VII a 
seventh. Having now obtained four other species, I have 
been led to consider whether this most remarkable group 
ought not to be removed from Triceratiwm altogether. The 
species are exclusively fossil, and confined to the Barbadoes 
deposit. Their structure is quite peculiar, bemg composed of 
one triangle within another, the space exterior to the inner 
triangle being simply a very broad border, divided into com- 
partments by transverse costee. In the angles is a more or 
less complex arrangement of a pseudo-nodule, with a blank 
space immediately beneath it, and often various short lines. 
With regard to the species, it is impossible to say whether 
the characters I have selected for the diagnosis are perma- 
nent, as I am not aware of any analogy to guide me, and our 
knowledge of the whole group is very limited. There 
appear to be two natural sections, in which the species may 
be arranged as follows : 
Srcr. I. Central triangle blank. 
Entogonia Abercrombieana, Grev.—Triceratium Abercrom- 
bieanum, Grev. ‘ Trans. Mie. Soc.,’ vol. ix, p. 83, Pl. X, figs. 
7—9. 
Entogonia inopinata, Grev.—Triceratium inopinatum, Grev., 
l. c., p. 84, fig. 10. 
Entogonia gratiosa, Grev.—Triceratium gratiosum, Grev., 
l. c., p. 85, figs. 12, 13. 
