MARYLAND GEOLOGICAL SURVEY 495 



BiDDULPHIA RETICULOSA GrunOW. 

 BiDDULPHIA SUBORBICULARIS GlUnOW. 



Plate CXXXIV, Fig. 11. 



Triceratium orbiculatnm Sbadbolt, 1854, Trans. Roy. Mic. Soc. London, p. 14, pL 



i, flg. 6. 

 Biddulphia angnlata Schmidt, 1875, Atlas der Diatomaceen-kunde, pi. cxli, figs. 7, 8. 

 Biddidphia suborbicularis Grun., Van Heurck, 1881, Syn. Diat. Belg. pi. c, figs. 



15, 16. 

 Biddtdphia suborbicularis Beyer, 1901, Proc. Acad. Nat. Sci. Phila., vol. lii, p. 705. 



Description. — ^Valve suborbicular, frequently with several irregular, 

 angular projections. Processes often unequal, inflated at the base and 

 truncate. Surface elevated half-way between the processes and center, 

 at which a depression occurs with reticulations from 5 to 8 in .01 mm., 

 increasing in size toward the circumference and radiating in slightly 

 undulating lines. Two, rarely three or four, stout spines are placed 

 obliquely opposite half-way between center and circumference. L. of s. 

 .089 mm. 



Occurrence. — Calvert Formation. 1 mile south of Chesapeake E. 

 E. Bridge, 1 mile northwest of West Eiver, 1 mile east of Marriott Hill. 

 Collection. — Maryland Geological Survey. 



BiDDULPHIA subrotundata Schmidt. 

 BiDDULPHIA tessellata (Grcville). 

 Plate CXXXIV, Fig. 12. 



Triceratium tessellatum Greville, 1861, Trans. Roy. Mic. Soc. London, toI. ix, p. 



71, pl. viii, fig. 14. 

 Triceratium robustum Greville, 1861, Trans. Roy. Mic. Soc. London, vol. ix, pl. viii, 



fig. 15. 

 Triceratium amoeimm Greville, 1861, Trans. Roy. Mic. Soc. London, vol. ix, p. 75, 



pl. ix, fig. 7. 

 Triceratium secernendum Schmidt, Atlas der Diatomaceen-kunde, pl. Ixxvi, fig. 34. 

 Biddulphia tessellata Boyer, 1901, Proc. Acad. Nat. Sci. Phila., vol. lii, p. 723. 



Description. — Valve triangular, with straight or slightly concave sides 

 and rounded angles. Surface usually some^diat convex at the center, with 

 rounded, elliptical, hexagonal or subquadrate reticulations about 3 in .01 

 mm., but smaller at the center, arranged in more or less concentric 

 rows and much smaller at the extremities of the angles which appear 

 hyaline under low magnification, where they are from 8 to 15 in .01 



