672 
Proceedings of Royal Society of Edinburgh. [sess. 
pi. v. fig. 5. — Circular, sometimes roundly elliptical. Diam. 
*075 mm. Surface convex, forming a low dome. Central space 
circular, about ‘015 mm. broad, sharply defined, hyaline. Markings 
large, areolate, increasing slightly to about semiradius, thence 
decreasing similarly to the border; around central space 4|, at 
semiradius 3 to 3| in *01 mm.; rows radial, straight; secondary 
oblique rows inconspicuous. Border inconspicuous. 
Habitat. — Springfield deposit, Barbados (Hardman). 
Yar. marginata , nov. Crasjpedodiscus ovalis, Grun., in Sch., Atl., 
pi. lxvi. fig. 6. — Roundly elliptical. Major axis # 065 mm., about 
1J times minor. Central space with small round, free granules. 
Markings areolate and subequal, 4 in -01 mm. for about -J of radius, 
on a distinct band adjacent to the border, round, granular, 8 in 
•01 mm.; interspaces between radial rows evident only on a band 
adjacent to border ; secondary oblique decussating rows more 
evident. — Porodiscus splendidus, var .1 Sch., ibid. 
Habitat. — Sprinfield deposit (Schmidt). 
P. nitidus. Grey., Trans. Micr. Soc. Lond ., 1863, p. 65, pi. iv. 
fig. 4. — Circular or subcircular. Diam. -05 to *07 mm. Surface 
uniformly and moderately convex. Central space circular or 
roundly elliptical, hyaline, *0075 mm. broad. Markings areolate, 
rarely obtusely angular towards the central space, increasing for a 
short distance outwards from this space, thence decreasing gradually 
to the border ; towards the central space 4 J, near the border 8, in 
*01 mm.; rows radial, straight, non-fasciculate. Border narrow. 
The markings being areolate, there are no such hyaline inter- 
spaces as are shown in Greville’s figure. Sometimes faint fasciculi 
are observed on one valve of a frustule, the opposite valve being 
non-fasciculate. 
Habitat. — Cambridge deposit, Barbados (Johnson !). 
Yar. armata , nov. — Diam. *0525 to *095 mm. Central space 
circular, *0075 mm. broad. Markings sometimes forming coarse 
moniliform strise towards the border ; spine3 acicular, about '01 mm. 
long, sometimes shorter, inserted about j of radius from centre; 
interfasciculate rarely a few at irregular intervals nearer the border. 
Girdle *0125 mm. broad in a valve *0525 mm. in diam., the 
