366 C. E Beecher — Cambrian Eurypterid Remains. 



and slopes off into the nearly flat pleural region without any 

 line of demarkation. The greatest width is across the third 

 segment. The extremities of the segments are rounded ante- 

 riorly and on the sides, and terminate behind as a simple angu- 

 lation. The first six segments are quite uniform in length, 

 while the three following are somewhat shorter, and the last 

 two are a little longer. 



Telson a broad flat spine, obtusely elevated along the mid- 

 dle. 



Surface smooth, with an indication of a row of minute 

 crenulations or scale-like markings near the posterior edge of 

 each segment. 



Dimensions. Greatest length of specimen 110 mm , length 

 exclusive of telson 82 mm ; greatest width, allowing for compres- 

 sion on left side, 60 mm ; length of cephalothorax 20 mm , width 

 49 mm ; greatest width of telson 17 mm . 



Formation and locality. From the lower members of the 

 Potosi limestone, Flat river, St. Francois county, Missouri. 



The only known genus of merostomes besides Strabops 

 occurring in the Cambrian is Aglaspis Hall, represented 

 by two species {A. Barrandi and A. Eatoni Whitf.). But 

 since Aglaspis belongs to the order Synxiphosura, it leaves 

 Strabops as the present sole representative of the Eurypterida.* 



* Although Aglaspis was compared with Limulus by Professor Hall, and its 

 affinities were distinctly stated as with the Merostomata, yet most subsequent 

 writers have overlooked its true relationships and have included it in their lists 

 of trilobite genera. The family named Aglaspidse was first employed in 1877 by 

 S. A. Miller in " The American Palaeozoic Fossils," p. 208, and the restoration of 

 the family to the Merostomata was first made by the writer in a paper entitled 

 "Outline of a Natural Classification of the Trilobites" (this Journal (4), vol. hi, 

 p. 182, 1897). 



EXPLANATION OP PLATE VII. 



Strabops Thacheri Beecher. — Dorsal side of type specimen x 3/2. Potosi lime- 

 stone (Cambrian), St. Francois county, Missouri. Original in Yale Univer- 

 sity Museum. 



• Yale University Museum, 

 New Haven, Conn., June, 1901. 



