A FOSSIL MARINE DIATOMACEOUS DEPOSIT. 137 



with rounded ends. Length of side to '003 ". This form is very 

 common on the deposit. 



T. eccentricum, n. sp., Gr. and St. — Valve with nearly straight 

 sides and very rounded angles. Processes prominent, situated on 

 one side of the angles formed by the sides. Surface of valve re- 

 ticulate. Length of side -003". (PI. XIV, Fig. 61.) 



T. arcticum, Brightwell. 



Note. — Herr Janisch informs us that the large form of this 

 species previously mentioned (" J. Q. M. C," Ser. ii, Vol. ii, p. 326) 

 is the same as T. permagnum, Jan., to be described and figured in 

 his forthcoming work on the Diatomaceas of the Gazelle Expedi- 

 tion. Through his kindness we have been enabled to examine an 

 authentic specimen of T. permaguum from Kerguelens Land, and 

 we have no doubt of the identity of the two forms. A large 

 quadrangular form of the same with very produced angles also 

 occurs in this deposit. 



The cellulation of these large Triceratia is rather smaller, and 

 the punctation of the pseudo-nodules more, delicate, than in the 

 usual form of T. arcticum ; but in all respects they exhibit the 

 features of the group, and we consider them as large forms of the 

 species. 



T. arcticum, Brightw., forma quinquelobata (T. quinquelobatum, 

 Grev., " T. M. S.," Vol. xiv, p. 83, PI. 9, Fig. 21).— Scarce. 



T. montereyi, Brightwell. — Having met with specimens of com- 

 plete frustules of this form since we recorded its occurrence, we 

 figure one showing the extreme convexity of the terminal valves 

 (PL XI, Fig. 25.) 



T.favas, Ehr., forma pentagona. —One or two examples of this 

 have occurred. 



T. grande, Brightw., forma quadrata. — Many of the quadrate 

 forms of the favus group, which are abundant in this deposit, are 

 convex, and in all respects, except outline, are so similar to T. 

 grande that we place them here. 



T. stokesianum, Grev. (" T. M. S.," Vol. xiv, p. 8, PI. 2, Fig. 

 23). — We have met with several specimens of a large Triceratium, 

 which resembles the form in the Briinn deposit identified by Prof. 

 Cleve ("J. Q. M. C," Vol. ii, Ser. ii, p. 169, PI. 12, Fig. 5) 

 with Greville's species. 



T.exornatum, Grev. (" T. M. S.," Vol. xiii, p. 9, PI. 2, Fig. 25). 

 — Scarce. 



