Geeville^ on New Diatoms. 
51 
extreme cases_, to introduce objects whose nature and position 
is a question of mere speculation. Few tilings have inte- 
rested me more,, iii; the course of the searching investigation 
now carried on for several years, than the variation of form 
and structure exhibited by diatoms evidently belonging to the 
Biddulphia and Hemiaulus groups. Of most of these the 
valves alone have been discovered, presenting only the front 
view; still, the characters are so prominently brought out 
that the family connection is undoubted, and a variation in 
the organs displayed, of which we had no previous conception. 
The eccentric-looking diatom now before us is totally un- 
like any recent species. The substance is smooth and hya- 
line, with thinly scattered spherical granules, which become 
more numerous and prominent on the processes. The latter 
are enormous in proportion to the rest of the valve, being 
each of them '0014'^ thick ; the upper part is thickly studded 
with minute puncta. Five slight convexities are found in the 
median space, separated by costse, which disappear just below 
the surface. Length of the valve figured '0075^'. 
Biddulphia corpulenta, n. sp., Grev. — Large ; valves in front 
view with the angles produced into short, thick, conical, ob- 
tuse processes, having a shoulder on their inner side; median 
surface convex, with slight elevations, separated by costse 
reaching nearly to the suture, and bifid at their extremities. 
(Fig. 16.) 
Hab. Barbadoes deposit, Cambridge estate ; in slides com- 
municated by C. Johnson, Esq. ; extremely rare. 
Another very extraordinary species, smooth and hyaline, 
with a few remotely scattered, faint puncta, and a close clus- 
ter of more minute puncta at the apex of the processes. The 
ends of the valve are not rectangularly straight, as in the 
preceding, but undulate. The costse are bifid at their base 
near the suture ; the apices divaricate and slightly incrassated, 
showing a curious afiinity with Porpeia, in which the costse 
are curved inwards and the ends thickened. The general 
appearance of the valve also approximates in some degree to 
some of the Porpeice. 
Biddulphia tenuicornis, n. sp., Grev. — Valve, as seen in 
front view, somewhat quadrangular, the angles produced into 
erect, long, almost filiform, obtuse horns; median space 
furnished with three long spines, one centrical, and one 
before each of the horns ; structure very minutely punctate. 
(Fig. 17.) 
Hab. Barbadoes deposit, Cambridge estate; in slides com- 
municated by C. Johnson, Esq. ; very rare. 
Not having seen the upper surface of the valve, I am un- 
