326 E. GROVE AND G. STURT ON 



reticulated structure. Not rare. Breadth over widest part, "0053". 

 (PI. XIX, Fig. 12.) 



C. Johnsonianus (Grew), CI. (Biddulphia Johnsoniana, Grew, 

 " T. M. S.," Vol. xiv, p. 6, PI. 2, Figs. 14, 15).— Small, rare, about 

 •003" in diameter. 



Triceratium capitatum, Ralfs. (Grew in " T. M. S.," Vol. ix, 

 p. 43, PI. 4, Fig. 10). — Frequent and more robust than Greville's 

 form. Distance between the angles, about •0027". 



T. parallelum (Ehr.), Grev. {forma trigona, A. Schm. " Atl.," PI. 

 75, Fig. 13, and PI. 76, Fig. 14-17. Quadrangular form = Amphite- 

 t ras parallela (Ehr.), Grev., «T. M. S.," Vol. xiii, p. 104, PI. 9, 

 Fig. 22). — Triangular form frequent, attaining a length between the 

 angles of '0077". The quadrangular form is also not uncommon, and 

 we have also observed the pentagonal variety. Not unfrequently a 

 triangular form occurs with very convex sides, in outline closely re- 

 sembling T. Harrisonianwn, Grev. in " T. M. S.," Vol. ix, p. 76, PI. 

 9, Fig. 9, but smaller, and without the characteristic veining. It can 

 be distinguished as " var. gibbosa." The figure in the " Atlas," PI. 

 81, Fig. 8, is very similar. 



T. Harrisonianum, Norm, and Grev. (Joe. cit supr.).— Our form 

 closely resembles the figure in the " Atlas," PI. 75, Fig. 16, and 

 should, we think, be classed with Stictodiscus. 



T. favus, Ehr. — The type form occurs rarely, but the quad- 

 rangular form T. favus var. quadruta, Grun. (Schm. " Atl.," PI. 

 84, Fig. 4,) is frequent, attaining a distance between the angles 

 of -008". 



T. favus var. maxima, Grun. (" V. H. Synop.," PI. 107, Fig. 5= T. 

 grande, Bright, " Q. J. M. S.," Vol. i, p. 249, PI. 4, Fig. 8).— The 

 triangular form is not uncommon in the heavier density, and nearly 

 approaches T. Grunovii, Jan., " Atlas," PI. 85, Fig. 5. Distance 

 between the angles, '012"; cellules, 3 to 3^ in '001". Surface 

 entirely covered with lines of granules 25 in '001", which radiate 

 from a central point. In some forms the cellules are smaller, not 

 two-thirds of the usual size. 



T. arcticum, Bright (" Q. J. M. S.," Vol. i, p. 250.— Quadrangular 

 form (T. arcticum var. californica, Grun. Schm,, "Atl.," PI. 81, 

 Fig. 4) not rare. The triangular form ("Atl.," PI. 79, Fig. 6) 

 also occurs, attaining a length between the angles of -013". 



T. castellatum, West (" T. M. S.," Vol. viii,p. 147, PI. 7, Fig. 3). 

 — Frequent. Some forms closely resemble T.umbilicatuni, Ralfs. 



