352 Proceedings of the Royal Society 
This arrangement enables the computer to examine any sin 
which he wishes to extract, so as to guard against any typographi- 
cal error; and, if the table of the multiples of 2verT were 
appended, to check readily the computation itself. When, how- 
ever, the differences have only a few figures, the ordinary method, 
of placing them in separate columns, is to be preferred ; it saves 
room, while the practised calculator has no difficulty in performing 
the requisite additions or subtractions. The utility of this arrange- 
ment has been long recognised. 
In the case of tables for common use, which are, in general, 
abbreviations of original calculations to a greater number of places, 
it is enough to give the first differences when these vary much. 
When such means of verification have been provided, the user of 
the table can make sure that the number which he extracts con- 
tains no error ; and if all users were to habitually make this 
examination, printed tables, and above all those printed from 
stereotype, would be gradually freed from errors of press. 
4. On an Unnamed Palaeozoic Annelid. By Professor Duns. 
(Plate IY.) 
Cyhaderma* (nov. gen.). — Generis Characters : — Corpus cylindricum, 
elongatum, nudum, striatum ; striae tenues, in ordinem undi ilatae, et ubique 
corpus cingentes, ita ut cutis subrugosa videatur ; linea doi sualis continua, 
alternasque cavaturas ovatus et vertices ostendens ; nulla ^ erorum articul- 
amentorum indicia ; vestigium tortuosum, bisulcum. 
Cymaderma (new genus). — Generic Characters: — Body cylindrical, 
elongated, naked, striated ; striae minute, waved symmetrically, encom- 
passing the form in all parts, and giving to the skin a subrugose appear- 
ance ; a continuous dorsal line, showing alternate oval depressions and 
slight ridges ; no traces of true articulations ; track, tortuous bisulcate. 
This annuloid fossil was obtained from upper Carboniferous strata, 
in a cutting on the Midland Railway, valley of the Kibble, near 
Settle, Yorkshire. Peculiarities characteristic of the striation and 
the median dorsal line led me to conclude that the form was pro- 
bably rare, or one that had not been described. It was thus of 
importance to get the other part of the slab on which the impres- 
* Etymol. Kv/xa, unda, B4p/xa, cutis. 
