358 Proceedings of the Royal Society 
depressions, deepest in the centre, and narrowing at each end, 
where they meet a slight ridge which stretches between the depres- 
sions, giving to the line, looked at from a short distance, a chain- 
like appearance. Were the branchial tufts of some recent annelids 
plucked out, we would have a somewhat similar appearance. 
Fourth , The characteristic striation. — This is most distinctly 
and even sharply marked on the form in the gritstone slab. It is 
also, though less definitely, marked on some of the softer micaceous 
slabs. Mr Hancock says, with reference to his specimen which has 
most resemblance to this — “ The transverse striae on the surface 
of the grooved form certainly gives it much the appearance of some 
organism but the value of this acknowledgment is lost by the 
supposition that the striae might have been “ produced by the in- 
termitting progress of the animal.” Now it is simply impossible 
that such striation as is seen here could have been produced in this 
manner. 
The expression 11 ondeleusement et symmetriquementf used by 
Cuvier in describing the striae on the shell of a cephalopode, very 
well indicates a leading feature of this striation. Indeed, the 
symmetry of these beautifully regular undulating striae may be best 
understood by comparing them with the striae on the shells both of 
recent and fossil nautilidse. Fig 3 is intended for a representation, 
ad naturam , of the characteristic striation, but the striae are sharper 
and better defined than shown on the figure. 
In conclusion, it will be seen that the distinctive features of the 
specimen now brought under the notice of the Society are the 
median dorsal line and the waved striation. In the generic features 
set down at the head of this paper, I have described the former 
thus, — linea dorsualis continua, alternasque cavaturas ovatas et 
vertices ortendens. As, however, uncertainty attaches to the 
nature of this line, the latter — the striation — may be taken as the 
outstanding generic feature, — striae tenues, in ordinem undulatae, 
et ubique corpus cingentes, ita ut cutis subrugosa videatur. The 
term Cymaderma, or wave-skin, is proposed for a genus, whose true 
zoological position is as yet uncertain. Should the examination of 
other specimens show that the oval depressions in the median dorsal 
line are only specific marks, not points of insertion of organs, and 
the striae mere lines formed by the contraction of the cutis — a most 
