104 
Greville, on Asterolampra. 
that it is desirable to restrict the appellation to those radi- 
ating divisions which_, commencing at the umbilicns^ are at 
first included between the umbilical lines and are afterwards 
continued in a contracted and linear form between the areo- 
lated segments to the margin. The umbilical lines {" sepi- 
menta imperfecta/^ of Ehrenberg) offer greater facilities for 
description than the bases of the rays themselves^ and a name 
for them could hardly be dispensed with. 
Several terms have been suggested for the narrow or 
" obsolete ^' ray which occurs in Aster omphalus and Spatan- 
ffidium ; but^ upon the whole, I prefer that of " median/^ 
which is as expressive as any of the others,, and has the 
advantage of having been already used by De Brebisson. 
An additional recommendation is, that it enables me to apply 
the equally expressive term, " median lines," to the two ap- 
proximated lines above the median ray, there being evidently 
some connection between these parts. The position of these 
lines differs in Asteromphalus and Spatangidium. In the for- 
mer genus they appear as really umbilical lines, approximated 
indeed, but still springing, like the rest, from the central 
point. In the latter they do not do so, and therefore cannot 
strictly be called umbilical lines. In fact, they have no rela- 
tion with the other lines in point of radiation. It was, 
therefore, desirable to invent a term which should be equally 
applicable in both genera. By the term median, then, I wish 
to imply the two lines which invariably accompany the me- 
dian ray, and only exist in connection with it. We shall see 
that much interest attaches to these lines, and that they 
afford good discriminative characters. 
Without giving the original characters verbatim, the three 
genera under consideration are distinguished as follows : 
Asterolampra, Ehrenb. in ' Berl. Monatsbericht,^ 1844, 
p. 73. The valve is strictly circular, with a centrical hyaline 
area, which is equally divided by lines [" sepimenta") radi- 
ating from the umbilicus. Each of these lines terminates at 
the base of a marginal areolated segment, while alternating 
with them the rays are continued between the segments to 
the margin. 
Asteromphalus, Ehrenb. in *^Berl. Monatsbericht,^ 1844, 
p. 198. The valve is exactly circular, with a centrical hyaline 
area ; but, instead of being equally divided by the lines 
sepimenta imperfecta") which radiate from the umbilicus, 
two of them are approximate and parallel ; and instead of all 
the rays being equal, one of them is much narrower than the 
rest, or, as Ehrenberg calls it, " deficiens vel ita obsoletus.^^ 
Spatangidium, De Breb. ' Bull, de la Soc. Linn, de Nor- 
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