RAYMOND: NEW AND OLD SILURIAN TRILOBITES. 21 



used the same name. When he came to figure a Wisconsin specimen, 

 however, he proposed a new specific name for it, and the name was so 

 obviously suggested by the Wisconsin specimens that I agree with 

 Weller that those specimens should be considered the types of B. ioxus. 



Professor Weller has suggested that the specimens from New York 

 may belong to another species. I have investigated the point as fully 

 as the material at my command would permit, and have not so far 

 been able to find any really good characteristics on which to base a 

 separation. The best specimens from New York are usually small, 

 and considerably flattened. The study of better material will prob- 

 ably reveal characteristics not now evident, and I have therefore 

 omitted from the synonymy the references to the New York specimens. 



Hall figured a pygidium which he assigned to the species, undoubt- 

 edly correctly, but up to the present the thorax has been unknown. 

 The M. C. Z. (Day collection), contains a large specimen, whose label 

 states that it is the "only perfect specimen found at Racine." It is 

 not exactly a perfect specimen, though it retains cephalon, parts of ten 

 thoracic segments and the pygidium. The axial lobe of the thorax 

 ,is somewhat less wide than one would have expected from the large 

 size of the animal, but, being 62% of the total width, is about the 

 general average among the bumastids. The pygidium does not show 

 an actual concave border, but there is a very decided flattening of the 

 curve of the profile at the back. 



As the specimen is preserved, the pygidium is somewhat unnaturally 

 drawn in, so that the actual length is not shown. On the other hand, 

 the last thoracic segment is displaced from the others and there is a 

 considerable space between the thorax and cephalon at the anterior 

 end, and between the thorax and pygidium behind. The length of 

 this specimen, therefore, gives only a rough approximation of the 

 correct length. Incidentally it should be noted that the cephalon of 

 this species has a large median tubercle near the posterior margin. 

 It is shown in Hall's figure, but omitted from Weller's. 



Measurements: — Length, about 180 mm.; cephalon 75 mm. long, 

 110 mm. wide; thorax about 75 mm. long, about 100 mm. wide at 

 middle, axial lobe 62 mm. wide; pygidium 65 mm. long, 102 mm. wide. 

 A well-preserved pygidium is 68 mm. long and 100 mm. wide. 



Formntion and locality: — Hall mentions Waukesha and Wauwa- 

 tosa as localities for this species, but in very extensive collections from 

 these places no specimens of this species are present, while we have a 

 number of specimens from the Racine dolomite at Racine, Wise. 



