MUSEUM OF COMPARATIVE ZOOLOGY, . 228 
from right to left,” The branchiæ of Cyamus diffusus Dall., 
Fig. 10, are described as “single, cylindrical, slender, with a 
very short papilliform appendage before and behind each bran- 
chia.” They are attached to the segments as shown in Fig. 10.* 
The simple branchia is much like that observed in many sec- 
tions of the 'Prilobite. Plate I. fig. 5, Plate II. figs. 2, 3. 
Figs.8,8 a. An enlargement of one of the sections of Ceraurus, showing the 
ova of the Trilobite. 
PLATE V. 
Figs. 1-3, Longitudinal sections of a Calymene. Figs, 1 and 3 are cut so as to 
intersect the legs beneath the lateral margins of the median lobe, 
and Fig. 2 along the centre of the median lobe and between the two 
sections showing the legs. Owing to the legs extending obliquely 
outward, the section cuts across the first two or three joints, and 
thus gives the peculiar pointed form. The cephalic appendages are 
not satisfaetorily preserved. One, however, in Fig. 2, is partially 
shown. Owing to an error in the figure but seven of the twenty 
transverse arches of the ventral membrane, beneath the median 
lobe, are represented in figure 2. 
Fig. 4 Oblique longitudinal section crossing the median lobe. Anteriorly 
the basal portions of the legs are seen, and then along the centre 
the section crosses to the opposite side, cutting in its passage the 
arches of the ventral membrane and posteriorly the appendages on 
the other side of the median line. It combines the features seen 
in the first three figures. The transverse arches of the ventral 
membrane are represented too thick and large. 
Fig. 5. Lateral view of an enrolled Calymene. The line a, a, is the general 
plane of the sections represented by Figs. 6-10, Plate I., and Fig. 
3, b, b, of Plate III. 
Fig. 6. Front view of the same. The line a, a, corresponding to Fig. 1; 
b, b, to Fig. 3 ; c, c, to Fig. 2; o, o, to Fig. 4, of Plate V. 
7. A young Limulus just after hatching from the egg. (Packard.) 
The legs are arranged as in the adult, and show the correspond- 
ence between the cephalic appendages of Euryplerus, Fig. 7, and 
those restored in the Trilobite, Plate VI. 
Fig. 7. The ventral side of the head of Zurypterus remipes. (Hall.) 
PLATE VI. 
ig. l. Restoration of the under or ventral surface of the animal inhabiting 
the dorsal shell of Calymene senaria. In making this restoration 
ier 
3 
* Proc. California Acad. Sei, Vol. IV. pp. 281-283, 1872. Illustrated in 
Marine Animals and the American Whale Fishery, Chas. C. Scammon, 1874. 
