C. L. Edwards 
259 
more than the 4 secondary peripheral holes are present, the additional tertiary 
ones are usually smaller (Fig. 61). It is to be noted that an asymmetrical distri- 
bution of peripheral holes prevails. 
The mean number of spines on the disc is "9 in the dorsal tables with a range 
of 0 — 10 and -3 in the ventral, with a range of 0 — 6. With the mean less than 1 
it is apparent that spines are not often found in any number. Sometimes the 
spines are large (Fig. 69), and again they may arise from a projection of some size 
(Fig. 68). Of the dorsal tables 22°/^ bear spines while only 11 of the ventral 
are so characterized, and thus the possession of spines cannot be considered normal 
in the species. Hence, as a diagnostic character of Semper's discarded variety 
amhoinemis, the possession of spines on the disc has no significance. 
The mean diameter of the disc is 50 /i in the dorsal tables, with a range of 
35 fi — 67 ^, and 43 fju in the ventral, with a range of 32 yu. — 58 ^. 
2. Height. 
The dorsal tables have a mean height of 54 /i., with a range of 32 /a — 72 fi ; the 
ventral 45 yu,, with a range of 24 /a — 81 //., and thus the dorsal tables are 20 7o 
higher than the ventral. 
3. Grown. 
The mean number of teeth is 12 in the dorsal tables, with a range of 8 — 16, 
and 12 in the ventral, with a range of 6 — 14. 
The mean diameter of the hole is 7 /u. in the dorsal crowns, with a range of 
3/i — 13 /i; 7 yu, in the ventral, with a range of 0 /x — \Q [x. In Fig. 76 this hole 
is large; in Fig. 79, small, while in some cases it is absent (Fig. 81). 
The mean diameter of the crown, not including teeth, is 19 /a in the dorsal 
tables, with a range of 13 /i — 22 fi; 19 /u, in the ventral, with a range of 10 fi — 22 ^ ; 
the diameter of the crown including teeth 39 in the dorsal tables with a range 
of 26 — 54 yu.; 36 yu. in the ventral, with a range of 22 /a — 51 /x. Taking one half 
of the difference between the two last determinations, the average lengfth of the 
teeth on the crown is 10 yu. in the bivium and 9 fi in the trivium. 
Thus from an examination of Table XVIII. it is found that the dorsal tables 
have more peripheral holes, spines and teeth, broader crown, larger crown-hole 
and longer teeth than the ventral tables, albeit the difference in some of these 
characters is very small. As shown by the standard deviations, the features of 
the disc are more variable in the dorsal tables, while the height and crown 
characters are more variable in the ventral tables. 
In the suckers of the dorsal pedicels are found what may be called reduced 
tables, in which only that central part of the disc immediately below and supporting 
the well-developed spire is pi-esent (Fig. 92). 
33—2 
