NO. 2 MIDDLE CAMBRIAN MEROSTOMATA 19 



CAMBRIAN MEROSTOMATA 



The only Merostomes heretofore known from Cambrian rocks 

 are from the Upper Cambrian formations of America. The first 

 discovered was described by James Hall in 1863 ' as Aglaspis 

 barrandi. Subsequently R. P. Whitfield described a second species 

 as Aglaspis eatoni." This genus was subsequently referred to the 

 sub-order Synziphosura of Packard.^ 



No Eurypterid remains were reported until in 1901 C. A. Beecher 

 described Strahops thachcri from the Upper Cambrian Potosi lime- 

 stone of Missouri.* 



Both Aglaspis and Strahops indicated that at the close of Cam- 

 brian time the Merostomata had advanced a long way toward a full 

 development of the sub-class and that a series of ancestral forms 

 had preceded them. It has been my desire for many years to 

 discover something of the older Merostome fauna in the Cambrian 

 and thus, if possible, secure further connections between the pre- 

 Cambrian Algonkian crustacean, Beltina^ and the great Merostome 

 fauna of the Silurian. 



In this paper two genera, Sidneyia and Amiella, are described : the 

 former, from very fine material, and the latter, from one broken and 

 imperfect individual. Both genera appear to belong to a sub-order 

 of the Eurypterida and it may be a distinct order. 



When preparing this paper I received from H. Mansuy, Geologist 

 of Indo-China, a series of photographs of Cambrian fossils from 

 Yunnan, and among them one of a fragment of a Merostome show- 

 ing six segments of the abdomen. From their form and surface 

 markings the species appears to belong to the genus Amiella- described 

 in this paper. (See p. 28.) 



Classification. — The two new genera, Sidneyia and Anrella, are 

 placed in the new sub-order Limulava of the order Eurypterida, 

 under the new family Sidneyidae. The relations of the order and 

 sub-order are shown in the following tabular view. 



^Sixteenth Ann. Rept. New York State Museum, 1863, pp. 181-182, pi. xi, 

 figs. 7-16. 

 ^Geol. Surv. Wisconsin, Vol. 4, 1882, p. 192, pi. 10, fig. 11. 

 ^Memoirs National Acad. Sci., Vol. 3, 1885, p. 151. 

 * American Journ. Sci., Vol. 12, 1901, pp. 364-366, pi. 7. 

 " Bull. Geol. Soc. America, Vol. 10, 1899, p. 238, pis. 25-27. 



