548 bulletin: museum of comparative zoology. 



with the neck-furrow by a curving constriction that is roughly parallel 

 to the axis of the glabella. The basal lobes are ovate and are separated 

 by a portion of the glabella which, in width, is less than one third the 

 width of the glabella at that point. The glabella is smooth, and the 

 cheeks are pitted. The sides of the glabella are usually parallel, but 

 may diverge slightly toward the front. The differences from Cheiru- 

 rus and from Ceraurus seem to be fairly constant, and this group seems, 

 therefore, to be worthy of generic rank. 



Description. — Ceraurinus is in general appearance and size much 

 like Cheirurus (genotype C. insignis Beyrich). The glabella is sub- 

 rectangular or expands only slightly. The posterior of the three pairs 

 of glabellar furrows are straight, about one third the width of the gla- 

 bella in length and slope gently backward. Their inner ends are con- 

 nected with the neck-furrows by curving constrictions which are about 

 parallel to the axis of the glabella. The constrictions are strong in 

 some species and very faint in others. The middle part of the axial 

 portion of the neck-furrow is parallel to the posterior edge of the neck- 

 segment. The outer thirds each slope gently backward. The eyes 

 are large for a cheirurid and are somewhat Asaphus-like. 



The thorax is presumably of eleven segments. The axial lobe is 

 slightly less than one third of the width of the thorax and tapers 

 gently backward. Each pleuron is divided by a node-like constriction 

 into a large inner third and a small outer two thirds. The inner third 

 bears a deeply impressed diagonal pleural furrow. 



The pygidium, well known only in Ceraurinus icarus (Billings), 

 is composed of three (four), segments ending in six free spines, which 

 are of about equal length. 



The type is Ceraurinus marginatum, sp. nov. 



Remarks. — The American species of this genus are Ceraurinus mar- 

 ginatus, sp. nov., Cheirurus icarus Billings, Ceraurinus trentonensis, 

 sp. nov., Cyrtometopus scofieldi Clarke, Cheirurus polydorus Billings, 

 and Cheirurus pompilius Billings. In the U. S. National Museum 

 there is a specimen from the Echinosphaerites limestone (C) of Russia, 

 which might almost be mistaken for Ceraurinus trentonensis, and 

 which also corresponds very closely to the descriptions of Cheirurus 

 ingricus Schmidt, and of Cheirurus ornatus Dalman. These latter 

 species seem to belong to this genus. From Barrande's figures, Chei- 

 rurus comes Barrande, would seem possibly also to belong to Cerauri- 

 nus. The genus may also be represented in India. Reed 1 places the 



i Ordovician and Silurian fossils from the Central Himalayas. Palaeontol. Indica, 

 1912, ser. 15, 7, Mem. 2, p. 10. 



