8i Greville, on New Diatoms. 



which I have had an opportunity of examining. By a reference 

 to the plate it will be perceived that some variation is liable 

 to occur in the lines at the angles^ as well as in the number 

 of the lateral costae. The puncta are considerably more 

 numerous than in T. marginatum. I have much pleasure 

 in dedicating this diatom to my acute correspondent, Dr. 

 Abercrombie, of Cheltenham. 



Triceratium inopinatum, n. sp., Grev. — Yalve with nearly 

 straight sides, rounded angles, and striated margin ; centre a 

 blank triangular space ; border divided by transverse costae 

 into minutely punctated compartments; a short line from 

 each angle of the central triangle terminating in a small, 

 roundish compartment, joined to the pseudo-nodule; no. 

 undulating line along the border. Distance between the 

 angles -0020". (Fig. 10.) 



Hab. Barbadoes deposit ; extremely rare. 



The only question Avhich can arise relative to the validity 

 of the present species is whether it be not a variety of the 

 preceding. Had the separation been proposed on account of 

 the apparently double pseudo- nodule alone, I should have felt 

 some hesitation. It might have been said that in one of the 

 varieties of T. Abercrombieanum the short lines proceeding 

 from the angles of the central triangle terminate in enclosed 

 spaces, owing to the incurved apices of the fork becoming 

 united ; and that if these enclosed spaces had been pushed 

 forward to a junction with the pseudo-nodule, we should just 

 have the appearance exhibited by the diatom now under 

 consideration. It may be remarked, however, that the 

 enclosed spaces above mentioned preserve their relative dis- 

 tance from the pseudo-nodule, as distinctly as if the apices of 

 the fork had remained open. In the present species there 

 is, at first sight, the appearance of an actual double pseudo- 

 nodule ; but it is an appearance only, the second one being 

 merely the fork of the short line meeting at the base of the 

 pseudo-nodule, and thereby indicating a diflFerent relative 

 position of the parts from what occurs in the preceding 

 species. In addition to what has been said, the total absence 

 of the undulating line so remarkable in the border of that 

 diatom seems to confirm the view I have taken of the pro- 

 priety of regarding T. inopinatum as distinct. 



Triceratium approximatum, n. sp., Grev. — Yalve with 

 straight sides, obtuse angles, and striated margin; centre a 

 blank, triangular space ; border divided by transverse costse 

 into punctated compartments ; a short line from each angle 

 of the central triangle terminating in a wide, shallow fork ; 

 pseudo-nodule single, sending out two spurs from the base ; 



