150 MEMOIRS OF THE NATIONAL ACADEMY OF SCIENCES. 
SYNOPSIS OF THE NORTH AMERICAN XIPHOSURA. 
Suborder XIPHOSURA. 
Family 1. CycLip@ Pack. 
Body disk-like, orbicular; abdomen composed of three segments, scarcely if at all differen- 
tiated from the cephalic shield; cephalic limbs nearly as in the larval Limulus; size small. 
Genus Oyclus De Koninck, with the characters of the family. 
Cyclus americanus Pack. 
Family 2. DIPELTID2 Pack. 
Body disk-like, elliptical ; abdomen differentiated from the cephalic shield, smooth, no seg” 
ments indicated. 
Genus Dipeltis Packard, with the characters of the family. 
Dipeltis diplodiscus Pack. 
Family 3. BELINURID Pack. 
Body limuloid in general shape; cephalic limbs as in the larval Limulus; shield with long 
slender genal spines ; abdomen with the segments distinct; caudal spine short or long. 
Genus Prestwichia Woodward. Eight abdominal segments, including the short caudal spine. 
Prestwichia dane Meek. 
Prestwichia longispina Pack. 
Genus Belinurus Konig. Nine abdominal segments, including the very long, slender caudal 
spine ; segments 7 and 8 consolidated. 
Belinurus lacoei Pack. 
Family 4. LoruLip 2 Zittel. 
Body longer than broad; abdomen with segments consolidated ; six pairs of abdominal limbs, 
five pairs having over a hundred pairs of gill-leaves. 
Genus Protolimulus Packard.* Seven abdominal segments, including the large thick caudal 
spine. 
Protolimulus eriensis (Williams). 
Genus Limulus Miiller. Cephaliclimbs large ; body longer than broad ; abdomen with 9 seg- 
ments; caudal spine longer than. the body. 
Limulus polyphemus (Linn.).t 
“In a notice of a new Limuloid Crustacean from the Devonian, Amer. Journ. Sc., July, 1885, p. 45, Prof. H. S. 
Williams described an interesting Limulvid from the Devonian of Erie County, Pennsylvania (associated with typical 
Chemung fossils). Itis described as Prestwichia eriensis, the author remarking that ‘“‘its identification with Prestwichia 
must be regarded as provisional.” He then adds: ‘ The following characters exhibited in the specimen are regarded as 
generic and as locating it with genus Prestwichia of Woodward: (1) the elliptical head shield; (2) the genal spines which 
proceed backwards more directly than inany described species of the genus; (3) the thoracico-abdominal segments anchy- 
losed to form a buekler, to which is attached (4) along telson. The general outline of the whole animal resembles that 
of the modern Limulus.” We have ventured, without having seen the specimen, to regard this form as probably a mem- 
ber of the family Limulida, and the forerunner of Limulus. It is certainly not a Prestwichia. The body is apparently 
longer than broad, and in outline it leaves a strong resemblance to the young Limulus after its first moult. This is 
seen in the shape of the abdomen and the caudal spine and in their relations to the rest of the body. It also seems 
probable that the abdominal segments were not free; in this respect it differs from the Belinurida, especially Prest- 
wichia. Judging by the number of lateral spines, the abdomen was composed of 6 segments exclusive of the caudal 
spine, thus differing from Prestwichia, which has 7, also from Limulus, which has8 pairs of lateral spines. We therefore 
venture to give it the generic name of Protolimulus, and to regard it as standing at the base of the family to which 
Limulus belongs. Its occurrence in the Devonian makes it a connecting link between the Upper Silurian Neolimulus 
and the Carboniferous and Jurassic Limuloids. We are indebted to Prof. Williams for the use of figures illustrating 
his P. eriensis. 
t Besides the American species, there are three others living, viz, L. moluccanus ; (East India) L. longispina Van 
der Hoven, Japan; L. rotundicauda Latr., Molucca Is, and Malacca. 
