274 BRIGHTWELL, ON TRICERATIUM. 



Synopsis of new Species. 



Section I. Sides concave, with angles protruded. Valvular 

 cells, minute. 



1. T. exiguum. Smith ; Smith's ' Brit. Diat.,' vol. ii., p. 87, No. 17.— 

 This very minute species, the only cue hitherto found in fresh water, has 

 been long known to the microscopists of this neighbourhood. It occurs in 

 fresh water at Ormesby and Horning, in this county, where it is not 

 uncommon. 



Plate XVII., fig. 1 a, h, c, end views ; d, front view. 



2. T. hrachiatum, n. s. — Angles drawn out into short thick arms, 

 bluntly truncated, and separated from the body by a distinct transverse 

 canaliculum. 



Barbadoes earth. Plate XVII., fig. 3 a, h, c, showing variations in size 

 and breadth of arms. 



3. T. irtmcatum, n. s. — Like the last ; but larger and stouter, and 

 having the surface of the frustule separated into twelve or more divisions, 

 by distinct lines or canaliculi, riuming horizontally from an irregular 

 central line, or canaliculum. 



Barbadoes earth. Plate XVII., fig. 4. 



4. T. venosum, n. s. — Larger than the last. Sides concave, ends rounded 

 oif. Canaliculi numerous, emanating from a central point in the frustule, 

 and diverging into two rows of irregular divisions on each side. 



Barbadoes earth. Plate XVII., fig. 5. 



5. T. coni/eriim, n. s. — Sides of the frustule irregularly concave ; the 

 angles being drawn out into an extended cone, recurved towards the end, 

 with a short stout horn near each end. Centre of the frustule convex, 

 with three stout setae ; one placed towards each angle. 



Shell cleanings ? Plate XVII., fig, 6 a, end view ; 6 h, front view. 



Section II. Sides straight, or somewhat convex. Valvular 

 cells, varying in size. 



6. T. favus, var. ^. — Cubical, four-sided, the sides somewhat concave, 

 and each of the four ends terminated with a stout horn. 



Sierra Leone ; mouth of River Eohelle. Plate XVII., fig. 7. 



7. T. formosum, var. y. 

 Bermuda earth. Plate XVII., fig. 8. 



I deem this to be the same variety as that found with the recent frus- 

 tules. The occurrence of such a form in a fossil or deposit state, has in- 

 duced me to give a figure of it. 



8. T. armatum, Pioper. 'Mic. Journal,' vol. ii., p. 283, fig. 1. — I possess 

 several forms from different localities, nearly allied to, or perhaps, varieties 

 only of this species. The figure in the ' Mic. Journal ' being unsatisfac- 

 tory, I have given front and end views of British specimens. 



Neyland, near Haverfordwest. Plate XVII., fig. 9 a, end view ; 9 b, front 

 view. 



9. Var. a. — Stout, and more convex than the British species ; valve 

 studded with numerous short spines, horns short and stout. 



Algerian deposit. Plate XVII., fig. 10. 



10. Var. ^. — Smaller than the last ; but like it in form, having throe 

 sjiines on the surface of the valve, one on the middle of each side. 



Australia. Plate XVII., fig. 11, an end view ; 11 h, front view square 

 variety. 



