668 
Proceedings of Royal Society of Edinburgh. [sess. 
{ Compartments 6, 5 equal smaller reaching to f- of \wyville- 
radius, the sixth larger, reaching to f of radius, / thomsonianus. 
Compartments otherwise, ..... 10. 
f Centro-lateral area ovate ; rays straight or slightly 
j flexed ; intervals not reaching border, . . . shadboltianus. 
10. -{ Centro-lateral area with sides more parallel, slightly 
concave outwards ; intervals attenuating slightly 
L reaching border, ....... Hookerii. 
[■Compartments reaching about f of radius inwards, 
longest at sides of subobsolete intervals ; rays 
8. -j straight ; intervals rapidly attenuating outwards, . stellatus. 
j Compartments reaching -f of radius inwards ; rays 
l towards subobsolete interval simply flexed, . . hiltonianus. 
C Centro-lateral area sharply constricted at middle, 
j thence expanding markedly outwards, compart- 
5. -{ ments reaching to § of radius inwards ; the inner 
| ends transversely truncate, . . . . . roperianus. 
I Centro-lateral area otherwise, ..... 11. 
Outer ends of intervals expanded, a distinct dark 
11. -j area at middle of wider portion, .... moronensis. 
k ISTo such intervals, ....... 12. 
^2 f Structure not markedly excentric, . . . . 13. 
' \ Structure markedly excentric, ..... 14. 
f Compartments with inner ends conical, ... 15. 
I Compartments with inner ends obtusely angular ; 
J intervals attenuating outwards, .... Beaumontii. 
' j Compartments with inner ends obtusely rounded or 
truncate ; rays sometimes simple, sometimes wavy ; 
L geniculations not regular, ..... Brookei. 
( Rays often dichotomous, bigeniculate at or within 
| their middle ; centrodateral area elongate, . . elegans. 
15. Rays simple ; the geniculations regular, forming an 
j elliptical figure round the centro-lateral area. 
L Centro-lateral area clavate, ..... imbricatus. 
14 / Subobsolete ray distinctly curved, .... reticulatus. 
‘ \ Subobsolete ray straight, ...... 16. 
( Centro-lateral area with sides parallel, and showing a 
16.4 deep regular median indentation, .... rams. 
t No such indentation, ...... 17. 
f Centro-lateral area 'short, broad, or subconical ; com- 
partments few, large; rays geniculate about their 
I middle. No lunate ridge, ..... Darwinii. 
17. \ Centro-lateral area subclavate or with sides slightly 
sinuate to almost parallel ; rays geniculate at or 
I beyond their middle ; a lunate ridge frequently 
L present at outer ends of intervals, .... heptactis. 
LIRADISCUS. 
Grev., Trans. Micr. Soc. Lond ., 1865, p. 4.— Circular, subcircular, 
or elliptical. Surface slightly convex or dome-shaped, flatter towards 
the border. Colour pale grey. Central space absent. Markings 
consisting of evident or more delicate lines, anastomosing irregularly 
or forming subregular or unequal areolae, on a more or less irregular 
