720 THE PALEONTOLOGY OF MINNESOTA. 



[Bumastus trentoncnsis. 



the smaller, now before us, the term Bumastus trentonensis, this process involving 

 simply the interchange of the generic names originally applied to the species. 

 The original of B. trentonensis was not described, but the wood cuts given of it 

 show in both views only eight thoracic segments. There is no evidence from these 

 figures that any of the segments have been lost or forced beneath one or the other 

 of the extremital shields. 



Mr. Billings' species Illccnus milleri (from various localities in the Trenton 

 limestone about Ottawa, and also from the Black River limestone in the township 

 of Hull, Canada) is inseparable from B. trentonensis. It was described as having 

 nine thoracic segments; Mr. Walcott, however, in identifying I. milleri in the Black 

 River and Trenton limestone of New York and the Trenton of Platteville, Wisconsin 

 (loc. cit.), suggests that one of the segments of the original was concealed, as his 

 specimens showed ten segments. Before me are two entire individuals of this 

 species from the Trenton limestone of Trenton Falls; one of them shows ten thoracic 



Fig. 32. Bumag'.us trentonensis Emruons (sp.). An entire individual with ten segments. Trenton 

 Falls, New York. 



segments, the other agrees with Emmons' original in having but eight. The latter 

 has been eroded in such a manner as to afford a complete longitudinal section of the 

 specimen, which fully demonstrates that no segment has been lost and that this 

 animal at this stage of development possessed no more than eight segments. An 

 enrolled individual from the Black River limestone at Poland, N. Y., shows nine of 

 these segments. 



Among the numerous examples of the species which have been received from 

 localities in Minnesota and Illinois, enrolled individuals are common, while but a 



Fi. 33. Bumastus trentonensis Emraons (sp.). An entire but, disjointed individual, with nine 

 segment--. 



single extended example has been observed. This, from the Galena beds at Pleasant 

 Grove, Minnesota, has nine segments; coiled specimens from the middle Trenton 



