No. 20. — A Revision of the American Species of Ceraurus. 

 By Percy E. Raymond and Donald C. Barton. 



The genus Ceraurus was proposed in 1832 by Green for a new tri- 

 lobite which he described as Ceraurus pleurexanthemus } The genus 

 has been accepted and used by American palaeontologists, with the 

 notable exception of Billings, and by a few European writers, among 

 whom were Roemer and Eichwald. The younger name Cheirurus, 

 proposed by Beyrich in 1845, 2 has, however, been preferred by nearly 

 all European palaeontologists. The description of this genus was 

 accompanied by the diagnoses of four species, Cheirurus insignis 

 Beyrich, Ch. claviger Beyrich, Trilobites sternbergi Boeck, and Ch. 

 gibbus Beyrich, and it is evident from the text that Beyrich had other 

 unnamed species in hand at the time. Of the four named species in 

 this article, Cheirurus claviger is the type of Corda's genus Eccopto- 

 chile, and Ch. sternbergi and Ch. gibbus are species of Salter's Crotalo- 

 cephalus. This leaves only the first species, Ch. insignis, to serve as 

 the type of Cheirurus, and it is evident from the description that 

 Beyrich based his genus almost entirely on this species. Beyrich was 

 familiar with Green's description of Ceraurus, but felt that the descrip- 

 tion and figure of that genus were so poor as to prevent its recognition. 

 Later, when Green's genus became better known through Hall's 

 figures, Beyrich's genus had become so familiar to European palaeon- 

 tologists that it retained their preference. The two genera have been 

 considered as essentially synonymous. We, however, believe that 

 this is not the case, and shall attempt to show that Ceraurus and 

 Cheirurus are distinct, although closely allied, genera. 



The genus Cheirurus, although originally used so broadly as to 

 include most of the Cheirurinae, has been restricted by the erection of 

 genera and subgenera, such as Eccoptochile and Actinopeltis Corda, 

 Cyrtometopus and Sphaerocoryphe Angelin. Finally it was re- 

 stricted by Schmidt 3 to those cheirurids in which there are always 

 eleven segments in the thorax, the inner part of each pleuron is cut 



1 Monograph of the trilobites of North America, 1832, p. 83. 



2 Ueber einige Bohmischen trilobiten. Berlin, 1845, p. 5. 



3 Revision der Oestbaltischen Silurischen trilobiten. Mem. Acad. imp. sci. St. 

 Petersburg, 1881, ser. 7, 30, p. 122. 



