NO. 9 NEW CAMBRIAN TRILOBITE FAUNULE — RASETTI 43 



the axial rings except the last have a median node. Pleural regions in 

 proximal portion not downsloping at all, convex and downsloping 

 only in marginal portion. Five pairs of pleural furrows very broad 

 and moderately deep ; narrow interpleural furrows well defined espe- 

 cially in the proximal portion. Border furrow broad and poorly 

 defined ; border flat, extended into several pairs of spines of about 

 equal size, evenly spaced, and directed perpendicularly to the margin. 

 All spines are broken and their length cannot be ascertained; the 

 bases of five pairs of spines are visible, but there must have been 

 another pair on the anterior, unpreserved portion of the border. The 

 distance between the spines of the sixth pair is much greater than the 

 distance between successive pairs. 



Surface of test with ornamentation that consists of shallow puncta 

 on the axial rings and becomes rather of reticulate type on the pleural 

 regions. Length of pygidium 6.0 mm, width 10 mm. 



Occurrence. — Collection cs-4, North Chatham. 



Discussion. — This pygidium is referred to Kootenia which it 

 resembles more than any other described genus, but its unusual fea- 

 tures might suggest a new genus if the cephalic parts were known. 

 Compared to the described forms of Kootenia, the axial rings are 

 proportionately much wider and shorter, the pleural regions are flat 

 rather than convex in their proximal portion, and the interpleural 

 furrows are unusually developed. In particular, there is little resem- 

 blance to the species of Kootenia or Fordaspis described from the 

 Lower Cambrian of the Taconic area (Lochman, 1956). 



Disposition of material. — Figured specimen: U.S.N.M. 146039. 



Genus BONNIA Walcott, 1916 



Type species. — Bathyurus parvulus Billings. 



Several species of Bonnia seem to be represented by cranidia, asso- 

 ciated with one form of pygidium definitely referable to the genus. 

 It cannot be determined whether all the cranidia belong to Bonnia 

 rather than to Kootenia, since the two are not always generically 

 distinguishable in the absence of the pygidium. For these reasons 

 each cranidium is described as an undetermined species of Bonnia 

 and the pygidium is not referred to any of the cranidia. 



BONNIA, species undetermined No. 1 

 Plate 11, figures 23-25 



Represented by several examples, mostly too immature for spe- 

 cific identification. Entire cranidium proportionately wide and short. 



