80 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 7)- 



border. Test thin, white to brown, smooth, occasionally with ob- 

 scure, very minute, crowded punctae. 



Dimensions: Length 5.1 mm., greatest height 3.9 mm., thickness 

 of entire carapace 2.2 mm. 



Remarks. — As alread}^ mentioned, this form is greatly like the 

 original figure of I. primaeva (Matthew). For reasons given it is 

 thought that this figure may not be entirely accurate, but in the 

 absence of the type specimen this point could not be determined posi- 

 tively. In the meantime, having referred to I. primaeva certain speci- 

 mens that are clearly distinct from this Arizona species, it became 

 necessary to apply a different name, namely /. faha, to the latter. 

 Even in the event that /. primaeva proves to have been correctly 

 figured by Matthew, the new name jaha may still be retained in a 

 subordinate sense, because the specimens to which the latter name is 

 here applied are relatively a httle higher than Matthew's specimen. 



Compared with other species of the genus described on preceding 

 pages, only /. labiosa is at all similar. Even this is easily distin- 

 guished, being longer and having a well defined ventral border. The 

 following /. carta is still shorter, but /. impressa is proportionately 

 longer and has an undefined, broad mesial depression. 



Occurrence. — Middle Cambrian, Bright Angel shale. Grand Canyon 

 of the Colorado, Ariz. Most of the specimens are from the Chuar 

 Valley. Three specimens from just above the massive sandstone of 

 the formation near mouth of Bass Canyon. The latter were asso- 

 ciated with most of the species of Walcottella described in this work. 



Cotype,s.— C&t. Nos. 56458, 56459, U.S.N.M. 



INDIANA FABA INTERMEDIA, new variety 



Plate 5, Figure 15 



A single specimen in a fair state of preservation differs too much 

 from average examples of I. jaha to be referred to it without quaUfi- 

 cation. With more specimens it might be distinguished as a good 

 species; but having noted but a single example, and this shghtly dis- 

 torted by pressure, it is thought best to separate it only as a variety. 

 Compared with the typical form of the species, it is found to be pro- 

 portionally longer, its ends more equally curved so that it is difficult 

 to distinguish the anterior from the posterior, the central part of the 

 surface less convex, and the punctae of the test more distantly ar- 

 ranged. The last fact possibly indicates more important genetic 

 dift'erences than can be made out with the material now available for 

 study. 



Occurrence. — Bright Angel shale, just above the lower massive 

 sandstone, Chuar Valley, Grand Canyon of the Colorado, Ariz. 



Holotype.— Cat. No. 56462, U.S.N.M. 



