1885.] Geology and Paleontology. 293 
taining it could not be ascertained when we discovered it in the 
‘dump’ or rock-pile.” 
s Cyclus americanus, n. sp—lIn a nodule from Mazon creek, 
Illinois, received from Mr. Lacoe, I recognize a species of this 
rather obscure genus which has not before occurred in North 
America, but is represented in Europe by nine species. 
In form C. americana is perfectly orbicular, the length being 
exactly equaled by the breadth. It is regularly disk-shaped, flat- 
tened hemispherical, with the edge of the body broadly and regu- 
larly emarginate, the margin being thin and flat, and apparently a 
little wider on the sides than on the anterior or posterior end. 
Length 14™™ breadth 14™™- 
None of the species yet described have had limbs, and nothing 
was known, so far as we are aware, of the nature of the limbs. 
Fortunately there are in Mr. Lacoe’s specimen traces of four, and 
perhaps five pairs of limbs, showing that Cyclus had short, stout 
are not preserved sufficiently well for us to ascertain whether 
ta ended in forceps, as in Limulus, or not, though they proba- 
did. 
nother fortunate discovery is that of the nature of the ceph- 
alic appendages of Euproops. In a nodule received from Mr. J.C. 
Carr, all the ambulatory limbs, except the first pair, are distinctly 
preserved, with faint traces of the shorter first pair which have the 
position and relative size of those of the larval Limulus just be- 
nurus stage. The species of Cyclus may be referred to a distinct 
family group for which we propose the name Cyclide. 
Dipeltis diplodiscus, gen. et sp. nov.—This name is proposed for 
a singular form which is not satisfactorily preserved, so that its 
exact relations are not readily determinable, though it will be 
recognizable as a Cyclus-like form. The body is suborbicular, flat- 
tened, disk-like, sloping regularly and gradually from the median 
area to the edge; it is divided into two portions; the larger one 
to be regarded as anterior or the cephalic shield, and the other as 
posterior, constituting the abdomen (urosome). The edge of the 
body is very slightly emarginate, not broadly so as in ree 
nor is the body distinctly trilobate as in the Limulidz, thoug 
