ON THE OARBONIFEROCrS XIPBOSTJROUS FAUNA. 153 



lu Pseudouiscus 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- 

 teridiB 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. Burypterida. 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 (Bntomostraca, 1785, p. 124), and adopted 

 by Fabricius (Ent. Syst., 487, 1893). 



The name Linmlus polyphenms (Linn.) was bestowed by Latreille in his Histoire Naturelle des 

 Crustac^s et des Insectes, torn. 4, p. 96, 1802. 



In 1798 Latreille, in Cuvier's Tableau 616mentaire de PHistoire 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 a Buffou, 

 Sonnini, Paris, 1798-1807) assigned Limulus to the Entomostracan order 1 Xiphosura (fide Milne 

 Edwards). 



In 1806 Latreille (Genera Grustaceorum et Insectorum, i, 10) placed Limulus in order 1 Xiphosura 

 of Legio 1 Entomostraca. 



In the same year Dumeril (Zool. Anal.) associated Limulus with Oaligus, etc. 



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 (Considerations g6n6rales, etc.) assigned Limulus a place under the Entomo- 

 straca in Family 1, Clypeaces, Aspidiota, associating it with Apus, Oaligus, and Binoculus. The 

 term Xii)hosura does not appear. 



In 1835 Latreille (Families naturelles du Rfegne Animal) places the Xiphosura between the 

 Phyllopods, the Trilobites, and the Siphonostoma. 



In 1828 Straus Durckheim (Considerations generales sur I'anatomie compar^e des Animaux 

 articules) referred Limulus to a new order, Gnathopoda, forming the eighth order of Crustacea, 

 which he placed between the Deca[)oda 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. Micr. Sc, 506, 1881) : 



Straus Durckheim maiutained that Limulus should be classified with the Arachnida, but the publication of his 

 views on the subject appears never to have talieu a very definite or satisfactory form. In fact, the only record of 

 Straus Durckheira's teaching on this subject which I can find is in the Frencli 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 volume, which bears the date 1829-1830, there is 

 a note headed " Sur I'appareil locomoteur passif des Arachnides," which appears to bean abstract of a memoir "On the 

 S. Mis. 154 20 



