610 
Proceedings of Royal Society of Edinburgh. [sess 
15, 
/'Markings areolate, at centre 3, at border 6, in 
J - 01 mm., irregular, 
| Markings rounded at centre, on a distinct band 
V. at border punctiform, oblique rows evident, 
lanceolatus. 
naviculoides. 
( Around border a circlet of prominent apiculi. 
Markings angular, 6 in ’01 mm., . 
Apiculi two, one at each end of minor axis. 
Markings minute, . . . ... 
16. -{ Apiculi prominent at intervals of '01 to '0125 mm. 
Markings towards centre rounded 6, at f radius 
angular 8, on a sharp band at border puncti- 
form 12, in *01 mm., , . . ... 
. Non-apiculate, . . . . , . 
spinulosus. 
sarmaticus. 
ovalis. 
18. 
f Markings rounded, granular, . . . . 19. 
' \ Markings angular, ...... 20. 
C An elliptical central area distinct, . . . oblongus. 
J An elongate, irregular, central hyaline area. 
' | Markings sometimes punctiform, . . , humilis. 
k Appearance otherwise, . . . 21. 
cy. / Markings without order, . . . . . 22. 
* \ Markings in more definite order, . . . 23. 
f Markings small, brilliant, granular, with wide 
| unequal hyaline interspaces. Valves elongately 
22. -j elliptical, tenuisculpius. 
I Markings 4 to 5 in ’01 mm. A broad hyaline 
k band adjacent to border, .... inexpedatus. 
23. 
f Markings on central portion subradial or irregular, 
on a well-defined band at border minute in 
radiating striae, .... . . 
Markings at centre irregular, elsewhere in rows 
slightly curved along, and parallel to major 
axis, diverging and bent away from minor 
axis, . . . . . . 
Markings punctiform, rows curved and diverging 
_ away from major axis, ..... 
ellipticus. 
lewisianus. 
elongatus. 
( An elliptical central area with markings in rows 
20.-! parallel to major axis, elsewhere rows radial, . obovatus. 
( No such central area, 24. 
f Valve elongately and irregularly elliptical. 
| Markings 6 to 7 in ‘01 mm. , . . . . paleaceus. 
2 . ! Valve regularly elliptical. Markings 4J to 5 in 
' j '01 mm., smaller at border ; rows curving out- 
wards from central area, thence parallel to 
l major axis, and again diverging outwards, . gracilentus. 
f Markings towards centre without order, with 
j wide interspaces, towards border in straight 
17. radial rows, 3 in - 01 mm.; apiculi curved, 
placed towards centre, ..... rex. 
L Appearance otherwise, . . . . . 25. 
f Markings areolate, delicate, central area distinct, 
ok J bounded by a ring of minute apiculi ; rows 
| radial. Valve readily overlooked, . . . praetor. 
kNo such central area, 26. 
