542 PROFESSOR E, RAY LANKESTER, 
fresh material, no such opportunity has yet presented itself 
of investigating the Scorpion. 
As to the shape of the lamellz, those of the pecten are 
narrower and relatively thicker than those of the lung-books 
or gill-books; the whole eighteen are also more nearly 
equal to one another in size and shape. In the lung-books 
the shape differs at the two extremities of the series a little, 
and in size the proximal lamine are much larger than the 
distal. The average shape may be described as that of a 
broad scythe-blade (Pl. XXVIII, fig. 8) with a narrow base 
support (@ 6). The lamellz of the gill-books of Limulus, 
on the other hand, are approximately semicircular in shape, 
with a wide base of origin (a8 in fig. 9, Pl. XXVIII). 
Moreover an important difference, which is explained by 
the convergence in place of divergence of the axis of the 
limb relatively to the mid line of the body, is seen when the 
lamellz of the gill-book and of the lung-book are compared, 
in the fact that in the gill-book the proximal lamine are 
the smallest (Pl. XXVIII, fig. 107’), whilst in the lunc- 
book they are the largest. 
Further comparison of the grouping and form of the — 
lamellz is facilitated by the figures on Pl. XXVIT1, where 
fig. 1 and fig. 1a, fig. 2 and figs. 2a@ and 10, fig. 3 and 
figs. 3a and 34, give representations of the three varieties of 
lamelligerous appendages in a series of identical positions. 
Fig. 1 should, for comparison with fig, 1 a, be \ocked at by 
inverting the plate. 
The axes which support the lamelle in the three varieties 
of lamelligerous limb differ much from one another, but in a 
manner directly corresponding with obvious functions. 
The pecten has a large free axis firmly chitinised, imper- 
fectly divided into two joints. It is flattened by antero- 
posterior pressure. The function of the pecten is not 
actually known, but it appears to be tactile. It is not 
respiratory, and the Scorpion is of terrestrial habit; hence 
its comparatively solid character and protective development 
of chitin. 
The gill-book of Limulus is supported on an axis, which 
is flattened by dorso-ventral pressure, protection being thus 
afforded to the otherwise naked and very delicate lamelle. 
It is not free except at its extreniity, where it exhibits a 
fointing of separate chitinous plates. Its base is very wide, 
and is attached, not to a flat sternal surface, but to an out- 
standing sternal lobe, which extends between the bases of 
fellow-appendages, and gives rise to a teat-like soft process 
in the median line (Pl. XXVIII, m d, fig. 10). The charac- 
