194 Proceedings of the Royal Physical Society, 
and arrangement of its ciliated appendages, and records of its occurrence. 
Certain new data are added, having reference to the dorsal and ventral 
median lobes of this larva and to the ciliated appendages of the larva of 
L. sarsi. 
The two species of Luidia which occur in British and western European 
seas (Sladen 28, p. 246) are Z. sarsi Diiben and Koren, and JZ. ciliaris 
(Philippi) Gray, the former having five arms and the latter seven. Both 
species have also a wide distribution within the Mediterranean (Ludwig 74). 
We may take it as an ascertained fact that the Bipinnaria asterigera of 
Sars is the larva of the five-armed form JZ. sarsi. Descriptions and figures 
of advanced stages in this larva have been given by various authors, e.g., 
Sars (26), Koren and Danielssen (72), Joh. Miiller (24, 1848, 1849), Mortensen 
(22), while Garstang (4) and M‘Intosh (78) have described and figured what 
are in all probability intermediate stages in its larval history. Bury 
(2, pl. v. fig. 18) has figured a corresponding intermediate stage from the 
Mediterranean, but we cannot say for certain to which of the two his 
larva belongs. 
In western European seas, the larva of JL. sarsi with the star already 
developed is by no means infrequent (Mortensen 27, p. 39), and recently 
I had the opportunity of making over thirty records of its presence in 
Echinoderm plankton material sent me by the Department of Irish Fisheries, 
and dating chiefly from the years 1903-06. The case is altogether different 
with the Bipinnaria asterigera of the seven-rayed form, L. ciliaris. Apart 
from simple references to its occurrence in the Mediterranean [ Metschnikoff 
20 (a bipinnaria with seven-rayed star); Ludwig 74, p. 440], there appears 
to be only one notice of its capture, a single specimen having been taken by 
the Ingolf Expedition in summer 1895, latitude 61° 2’ north, and longitude 
40’ east (Mortensen 2/, p. 40). The specimen—a relatively large one—was 
identified by Ludwig, who concluded that it could not belong to any species 
except LZ. ciliaris (Mortensen /.c.). The larva in question had been preserved 
in Fiemming’s solution, and was so much contracted that Mortensen was not 
able to make a proper drawing of it, or to determine the number of its ciliated 
appendages. He stated, however, that the dorsal and ventral median lobes 
or processes were of approximately equal length, and that both were simply 
rounded at their extremities—a contrast with JZ. savsi in which the dorsal 
median lobe is much longer than the ventral one and ends in an expansion 
which is cordiform or heart-shaped, 7.e., showing a notch in the middle line 
anteriorly. Elsewhere (22, p. 10) he puts it as probable though not certain 
that the larva of Z. ciliaris has a smaller number of ciliated appendages than 
that of ZL. sarsi, a “middle dorsal” process being present in the latter, but 
