X 



A FOSSIL MARINE DIATOMACEOUS DEPOSIT. 329 



Greville's type form in " T. M. S.," Vol. xiii, p. 6, PL 2, Figs. 23 

 and 24. From three to nine vein-like lines project from each side, the 

 granules are more numerous and closer set, and the processes are 

 not so elongated. The connecting membrane is similar. Distance 

 between the angles, • 009-1" ; a smaller form also occurs. (PI. 

 XIX, Figs. 17, 18.) This may, perhaps, on further consideration 

 require separation from Greville's species. 



T. cancellatum, Grev. (" T. M. S.," Vol. xiii, p. 9, PI. 2, Fig. 

 17). — This form, which occurs not unfrequently, corresponds to 

 Greville's description, but not to his figure. The sides of the 

 valve are nearly straight ; the six alternate radiating elevations 

 and depressions are distinct in some forms, while in others they 

 are scarcely, if at all, perceptible. The commencement of two 

 vein-like lines, projecting inwards from the sides, are usually 

 quite distinct. As we are in doubt whether our determination is 

 correct, we give a figure at PI. XIX, Fig. 19. 



T. spinosum. Bail, var. ornata, n. var. Gr. and St. (T. spinosum, 

 Bail, A. Schm. " Atl.," PI. 87, Figs. 2, 3).— This form has a great 

 resemblance to Amphitetras ornata, Shabbolt, " T. M. S.," Vol ii, p. 

 16, PI. I, Fig. 10, the quadrangular form of, and identical with, T. 

 pentacrinus, Wallich " Q. J. M. S.," Vol. vi, p. 250, PI. 12, Figs. 

 10-14. (As Greville has a T. ornatum, in order to prevent confusion 

 AVallich's specific name, though later in date, had better be 

 adopted.) In other respects, however, this form is nearer to T. 

 spinosum. We have only observed the triangular form, which has 

 straight or slightly concave sides and horn-like processes at each 

 angle ; the centre is slightly inflated, and the surface of the valve 

 is covered with markings resembling those of T. pentacrinus ; but 

 with the addition of four or more spines, which are usually broken 

 off. Distance between the angles -0032 . (PI. XIX, Fig. 20.) 



DESCRIPTION OF PLATES. 

 Plate XVIII. 



Fig. 1. Navicida sparsi punctata, Gr. and St., n. sp., ^— . 

 „ 2. „ interlineata, Gr. and St., n. sp., ^. 



„ 3. Gh/phodesmis marginata, Gr. and St., n. sp., ~~. 

 „ 4. Rutilaria radiata, Gr. and St., n. sp., ^. 



5; 5 }} outline of small form showing variation in 



the shape, ^. 

 „ G. „ lanceolata, Gr. and St., n. sp., i^. 



Journ. Q. M. C, Series II., No. 16. c c 



