1888-89.] Mr John Rattray on the Genus Coscinodiscus. 6 75 
centre, towards the border subplain. Central space roundly 
elliptical, with major axis about ’01 mm. long, and corresponding 
in direction to minor axis of valve, delicately punctate. Markings 
areolate, gradually increasing from central space outwards ; towards 
the central space 6 or 6|, towards the border 4 to 4J, in '01 mm.; 
rows radial, straight ; secondary oblique decussating rows indistinct. 
Border narrow, hyaline. 
Habitat. — Pacific Ocean, from a sounding made at the equator 
by H.M.S. Challenger (Castracane). 
P. conicus. Grev., Trans. Micr. Soc. Lond.. 1863, p. 65, pi. iv. 
fig. 3. — Diam. '025 to '0525 mm. Major axis of frustule from 
'0625 to '0875 mm. Surface a more or less elongate regular cone, 
transversely truncate at the extremities, the opposite valves of a 
frustule of unequal height. Central space ? Markings obtusely 
angular or subareolate, 6 in '01 mm., subequal; rows radial, 
straight, non-fasciculate ; secondary oblique decussating rows 
evident, from the truncated ends of the cone a few short tapering 
clear lines, distinct. Girdle cylindrical, from '025 to '0325 mm. 
broad ; a narrow band at each extremity, hyaline, the intervening 
portion clouded with diffuse parallel lines. 
Habitat. — Cambridge deposit, Barbados (Johnson !) ; Bar- 
bados (Johnson ! Greville !) ; Bridgewater deposit, Barbados 
(Johnson[!). 
P. hirsutus. Grove and Sturt, Jour. Quek. Micr. Cl., 1887, 
p. 143, pi. xiv. fig. 54. — Circular. Diam. '075 to '0875 mm. 
Surface flat from central space to the sharply-defined marginal 
band, the latter sloping gently to the border. Central space 
circular, sharply defined, \ to -J- of diam. broad, surrounded by a 
narrow, more hyaline, sometimes interrupted band, with irregular 
outer edge. Markings rounded, prominent papillae, with hyaline 
interspaces and without order ; processes hour-glass-shaped, at sub- 
regular intervals, inserted on inner edge of marginal band, between 
these processes delicate radial striae, 6 to 8 in '01 mm., extending 
outwards to about middle of band; adjacent to border a circlet of 
evident papillae at intervals of '0075 to '01 mm. Border narrow, 
bearing minute granules, 6 in '01 mm. 
