Trilobites of thk Cha/v T.i.mesione. .357 



Another cranidium : length 15.5 mm. ; width 24 mm.; middle lobe 

 5 mm. wide behind ; 13.5 mm. wide in front. 



A pygidium : length 8 mm.; width 11.5 mm.; axis 5 mm. long. 



Another pygidium: length 16 mm.; width 22 mm.; axis 9 mm. 

 long. 



Locality. — Occurs in middle and upper Chazy on Valcour Island, 

 also at Chazy and Cooperville, New York ; Isle La Motte, Vermont ; 

 Montreal and Mingan Islands, Canada. Figure i is from a specimen 

 in the Carnegie Museum. Figures 2 and .3 are from specimens in 

 the writer's collection. 



I'am i ly A C 1 1 ) AS PI D.F: IJarrande. 



(lenus ACIDASPIS Murchison. 



Subgenus Claphurus ' (name proposed). 



There are, in the Chazy limestone, two species of trilobites which, 

 from their general characters must be placed in or near the genus 

 Acidaspis, yet which do not conform to the definitions of any of the 

 subgenera of Acidaspis now in use. Clarke, in his " Note on Aci- 

 daspis," Forty- fourth Annual Report of the New York State Museum, 

 1892, distributed the American species of Acidaspis among several 

 subgenera, all the Ordovician forms going into his division Odonto- 

 pleura. The Chazy forms differ from Odontopleura, and, in fact, from 

 all species of Acidaspis, in having eleven or twelve segments in the 

 thorax, and a pygidium with an aspinose margin. 



According to Hall's figures, Acidaspis treiitoiiensis is w^ithout spines 

 on the posterior margin of the pygidium, but comparing its structure 

 with the pygidium of Odontopleura parvi/la \Valcott and other species 

 it seems probable that, when perfect, the dorsal ridges of the pygidium 

 extended beyond the margin as spines. 



The type of this subgenus is Arionelliis piistulatiis Walcott. 



Glaphurus pustulatus Walcott. (Plate 14, figures 4-6. ) 



Arionellus pustulatus Walcott, 1S77, Advance Sheets Thirty-first Annual Report 

 New York State Museum Natural History, page 15. 



Arionellus pustulatus Walcott, 1879, Thirty-tirst Annual Report New York State Mu- 

 seum Natural History, page 68. 



1 Glaphurus. Derived from the Greek verb y/ji(^(,>, the root of which is used in the 

 noun y/.novpiu, meaning smoothness, and the noun o'vpti, meaning a tail. 



