ON THE CARBONIFEROUS XIPHOSUROUS FAUNA. 145 
tigations of Dr. Lockwood and myself, “these forms may indeed be the larval stages of Prestwi- 
chia, Belinurus, ete., the antetypes in Carboniferous times of the modern king crab.” “ Were it 
not for the large size of these fossils, some (C. Harknessi) measuring five lines in length, three 
and one-half lines in breadth, and three lines in height, we should be disposed to agree with 
Mr. Woodward; but, from what is known of the size and form of the freshly-hatched larva of Lim- 
ulus and the Trilobites, I should infer that they were either the larve of some unknown genus of 
Limulide, or adult but embryonic forms. The larve of Belinurus and its allies, Prestwichia and 
Euprooéps, were, in all probability, closely allied in their form and size at the time of hatching to 
the larva of Limulus. But on comparing the deep hemispherical form of Cyeclus, with the surface 
of the body deeply lobed over a more or less extent, with the embryo of Limulus before it is 
hatched (PI. iv, figs. 18, 18a), we find a striking similarity; indeed, we seem to be dealing with a 
distinct embryonic type of Limulide. In Cyclus we have, in a tate larval or possibly adult condi- 
tion, that state of Limulus in which the body is deeply hemispherical, and the abdomen has just 
been differentiated from the rest of the body, while the deep transverse lobes of the yolk are not 
yet absorbed, as seen in Pl. iv, figs. 18, 18a, in the embryo of Limulus; the cardiac or median lobe 
being as distinctly marked in Cyclus as in the embryo of Limulus.” (Development of Limulus, 
1872, p. 189.) 
After again reviewing the characters of Cyclus, with the specimen of C. americanus before us, 
we feel confirmed in the views above presented, and would regard Cyclus as the representative of 
a family of Xiphosura, being an adult form, and embryotypic, to coin a word, of a Limulus, while 
the Belinuridsz represent the larval Limulus. 
Family DIPELTID4 Packard. 
DIPELTIS DIPLODISCUS Packard. PL V, figs. 2, 2°. 
Dipeltis diplodiscus Pack., Amer. Naturalist, xix, 293, March, 1885. 
This name was proposed for a singular form which is not satisfactorily preserved, so that its 
exact relations are not readily determinable. The body is suborbicular, flattened, disk-like, slop- 
ing regularly and gradually from the median area to the edge; it is divided into two portions; the 
larger one to be regarded as auterior or the cephalic shield, and the other as posterior, constituting 
the abdomen (urosome). The edge of the body is very slightly marginate, not broadly so as in 
Cyclus; nor is the body distinctly trilobate, as in the Belinuridee and Limulide, though unfortu- 
nately the median area of the cephalic shield is wanting. The integument is rather thin, showing 
no traces of segments; its surface may have had a few scattered small tubercles, at least there are 
slight indications of them. The surface is smooth and shining. 
The cephalic shield is nearly twice as broad as long; the posterior lateral angle is well-rounded, 
with no sign of a lateral spine; in front the edge was probably obtusely rounded; the surface is 
slightly convex, the disk being low and flat, with no traces of a glabella; the hind edge of the 
shield is moderately concave, the limits between it and the urosome being clearly indicated by a 
slight, but distinct, regular, curvilinear suture. 
The urosome is about three-fourths as long as, but equal in width to the cephalic shield. The 
front edge is somewhat arcuate, so that the projecting anterior-lateral angle is directed a little 
forward, and is quite free from the lateral angle of the cephalic shield, which turns away anteriorly 
from it, leaving a triangular space between the sides of the two regions. Posterior edge of the 
urosome regularly rounded, and with a slight margin. No traces of a caudal lobe or spine. Total 
length, 20""; total breadth, 20"; length of cephalic shield, 11°"; breadth, 26""; length of urosome, 
9°"; breadth, 19.5"". Collection of R. D. Lacoe, 2017 *”* in a nodule from Mazon creek, Morris, 
Illinois. 
This remarkable animal was disk-like in shape, composed of two regions, the head and abdo- 
men or urosome, which are more distinctly separated than in the Cyclide ; while there are no posi- 
tive characters to separate it from this group, we would, for the present at least, refer it to an 
allied family, as it is orbicular, tailless, and consists of a broad, large cephalic shield, with a shorter, 
distinct, non-segmented urosome. 
S. Mis. 154 19 
