X 



A FOSSIL MARINE DIATOMACEOCS DErOSIT. 327 



(" Pritch.," p. 854. Bchm. " Atl.," PI. 94, Fig. 11). It would 

 seem that these two cannot be specifically distinguished. 



T. rotundatum, Grev. (" T. M. S.," Vol. ix, p. 75, PI. 9, Fig. 

 6). — Rare, but identical with Greville's figure. 



T. venosum, Bright (" Q. J. M. S.," Vol. iv, p. 274, PI. 17, 

 Fig. 5). — Occurs sparingly. 



T. coscinoides, Gr. and St., n. sp. — In outline this form, which is 

 very common, resembles T. cinnamomeum, Grev. (" Q. J. M. S.," 

 Vol. iii, N. S., p. 232, PI. 9, Fig. 12 — Cestodiscus cinnamomeus , 

 Grim. " V. H. Synop.," PI. 126, Fig. 1), but in other respects is 

 quite different. The surface is covered with small hexagonal 

 cellules, which are larger at the centre but gradually decrease in size 

 towards the margin. Greville's form is a true Cestodiscus, with 

 puncta and distinct marginal spines, entirely wanting in our form. 

 Distance between the angles, -0022" to -004" ; cellules about 

 12-13 in -OOr. (PI. XIX, Fig. 13). 



This form seems only to be a three-angled Coscinodiscus. Gru- 

 now, in the " Franz. Jos. Land Diat.," p. 31, mentions a similar 

 form from the Mors deposit, for which he proposes a subgenus 

 " Pseudo-triceratium " ; to this our form would belong. 



T.partitum, Grev. (" T. M. B.," Vol. xii, p. 14, PL 2, Fig. 8).— 

 Differs from Greville's form in its larger size and greater convexity 

 of the sides, which in his description are stated to be " slightly 

 concave " ; but in other respects resembles it so closely that it 

 would hardly be advisable without further investigation to create a 

 fresh species. Distance between the angles, *005". 



T. divisum, Grun. ( " V. H. Synop.," PL 113, Fig. 8).— Rare. 

 Distance between the angles, •0021". A well-defined species, 

 differing from T. partitum, Grev., in the septa being continuous, 

 without the faint interruption in the middle, and in the absence of 

 the second septa, cutting off the angle itself. 



T. Kinkerianum, Witt ( " Simbirsk," p. 33, PL 8, Fig. 10).— Not 

 unfrequent. A variety of Witt's species, closely resembling the 

 figure in the " Atlas " (PL 95, Fig. 17), but larger and more robust, 

 with prominent angles, covered with fine puncta. Distance between 

 the angles, '0054". As this, on further investigation, may require 

 to be separated from Witt's species, we give a figure at PL XIX, 

 Fig. 14. 



T. venulosum, Grev. ("T. M. S.," Vol. xii, p. 90, PL 13, Fig. 21). 

 — Very much larger than Greville's species, and might be distin- 



