1888-89.] Mr John Rattray on the Genus Coscinodiscus. 671 
L. minutus. Grev. (Trans. Micr. Soc. Lond ., 1865, p. 47, pi. v. 
fig. 6), belongs to Cresswellia. The surface of the type is dome- 
shaped, and the markings on the central portion regular, and areolae 
3J to 4 in '01 mm. 
Artificial Key. 
, f Outline circular, ....... 
’ \ Outline elliptical, 
( Lines not anastomosing. Border broad, striae 15 in 
2.4 '01mm., 
f Lines anastomosing, ...... 
f Areolae unequal, 1 to 3 in '01 mm. Band adjacent to 
, J border subregular, . . . 
' 1 Areolae unequal, few ; around border the lines radial or 
l subradial, often dichotomous, .... 
f Extremities of major axis acute. Surface slightly 
„ I convex. Markings delicate, areolae 2 to 3J in 
] '01mm. Band adjacent to border narrow, . 
I Extremities of major axis not acute, .... 
f Surface slightly convex, ...... 
_ J Surface markedly convex. Markings prominent, 
‘ 1 areolae often imperfect at centre ; apiculi acicular, 
l irregular, inserted at angles of areolae, . 
f Markings delicate, 4 in '01 mm., subequal; non- 
apiculate. Border narrow, sharply defined, . 
6. Markings evident ; marginal band of areolae distinct, 
its outer edge crenate ; areolae unequal, irregular, 
f 2 to 3 in '01 mm., largest at the centre, 
PORODISCUS. 
Grev., Trans. Micr. Soc. Lond., 1863, p. 63. — Valves elliptical, 
circular or rhombic : sometimes the opposite valves of a frustule of 
unequal sizes. Surface slightly convex, dome-shaped or conical, with 
transversely truncated ends. Colour pale smoky grey. Central 
space circular to roundly elliptical, faintly punctate or hyaline, 
its outline smooth or finely crenulate. Markings small, round, 
granular, papilliform, or areolate ; rows radial, more rarely 
inconspicuous or undifferentiated, secondary oblique rows some- 
times evident ; fasciculi frequently distinct ; interspaces largest 
near the central space, sometimes absent ; spines long, acicular or 
hour-glass-shaped, frequent ; a sharply defined marginal band rare. 
Border inconspicuous. — Craspedodiscus , pro parte, Grun.; Sch., Atl., 
pi. lxvi. figs. 7-9 ; Craspedoporus, pro parte, Grove and Sturt, 
Jour. Quelc. Micr. Cl., 1887, p. 67. 
2 . 
3. 
capensis. 
4. 
barbadensis. 
furcatus. 
ellipticus. 
5. 
6 . 
ovalis. 
oblongus. 
marginatus. 
P. splendidus. Grev., Trans. Micr. Soc. Lond., 1865, p. 46, 
