ON THE CARBONIFEROUS XIPHOSUROUS FAUNA. 153 
In Pseudoniscus we have another form which suggests a relationship to the Trilobites. Our 
figure is copied from Woodward’s restoration. Nieszkonski, the original describer, remarked, 
“On the inner side of the shield we notice a place cut out, with the convexity looking outward, 
which should certainly be regarded as the outer edge of the eye.” 
The foregoing remarks are suggested by a study of the figures and descriptions of these remark- 
able forms, and as they are not based on a study of the specimens themselves, they will be taken 
only for what they are worth. But the fact remains that we have, side by side with the Euryp- 
teride in the upper Silurian strata, a group which does not apparently belong to either the Euryp- 
terida or genuine Xiphosura of the Carboniferous and later periods, and to which it seems best to 
assign, temporarily at least, an intermediate position. The group also is of great interest as 
serving to bridge over the gap between the Merostomata and Trilobita. 
The following view will express the relations of the three suborders : 
Order MEROSTOMATA. 
1. EHurypterida. 2. Synziphosura. 3. Xiphosura. 
HISTORICAL REVIEW. 
I.—History of the Xiphosura. 
In 1764 Gronovius, in the second fasciculus of his Zoophylacium Gronovianum, p. 220 (according 
to Van der Hoeven, for we have not seen this work), proposed the name Xiphosura. His work 
appeared in three fasciculi, bearing date 1763 to 1781, the second fasciculus dated 1764. 
The name Limulus was first proposed by O. F. Miiller (Entomostraca, 1785, p. 124), and adopted 
by Fabricius (Ent. Syst., 487, 1893). 
The name Limulus polyphemus (Linn.) was bestowed by Latreille in his Histoire Naturelle des 
Crustacés et des Insectes, tom. 4, p. 96, 1802, 
In 1798 Latreille, in Cuvier’s Tableau élémentaire de ’ Histoire Naturelle des Animaux, placed 
the Limuli in the Crustacea, under the Monoculi. 
-Previous to 1806, the exact year we have not been able to ascertain, Latreille (Suite 4 Buffon, 
Sonnini, Paris, 1798-1807) assigned Limulus to the Entomostracan order 1 Xiphosura (fide Milne 
Edwards). 
In 1806 Latreille (Genera Crustaceorum et Insectorum, i, 10) placed Limulus in order 1 Xiphosura 
of Legio 1 Entomostraca. 
In the same year Duméril (Zool. Anal.) associated Limulus with Caligus, ete. 
In 1809 W. Martin “ gave a figure and short description of a Limulus crustacean from the coal 
measures, which he included with the Trilobita.” 
In 1810 Latreille (Considérations générales, etc.) assigned Limulus a place under the Entomo- 
straca in Family 1, Clypeaces, Aspidiota, associating it with Apus, Caligus, and Binoculus. The 
term Xiphosura does not appear. 
In 1835 Latreille (Familles naturelles du Régne Animal) places the Xiphosura between the 
Phyllopods, the Trilobites, and the Siphonostoma. 
In 1828 Straus Durckheim (Considérations générales sur Vanatomie comparée des Animaux 
articulés) referred Limulus to a new order, Gnathopoda, forming the eighth order of Crustacea, 
which he placed between the Decapoda and Arachnida. 
After the publication of his “Considerations,” Straus-Durckheim removed the Gnathopoda from 
the Crustacea to the Arachnida, as will be seen by the following extract from Lankester’s “ Lim- 
ulus an Arachnid” (Quart. Journ. Mier. Se., 506, 1881) : 
Straus Durckheim maintained that Limulus should be classified with the Arachnida, but the publication of his 
views on the subject appears never to have taken a very definite or satisfactory form. In fact, the only record of 
Straus Durekheim’s teaching on this subject which I can find isin the French translation of Meckel’s ‘‘ General Treatise 
on Comparative Anatomy.” MM. Reister and Alph. Sanson carried out this translation and added many notes in the 
form of appendices to each volume. At the end (p. 497) of the sixth yolume, which bears the date 1829-1830, there is 
anote headed ‘‘Sur l’appareil locomoteur passif des Arachnides,” which appears to be an abstract of amemoir “‘On the 
S. Mis. 15420 
