PRIMORDIAL PERIOD. 30, 



Length of body from two and ;i lialf to seven and a half centimeters. 



It is not improbable that the form represented by figure 2 h and c is 

 specifically distinct from the form represented by figure 2 a, especially as the 

 first-named form is quite a constant one among the specimens of the collec- 

 tions. I have, however, not felt fully warranted by the collections yet 

 made in separating them under a difterent specific name, but I have selected 

 the form represented by figure 2 a as typical of the species here described. 



Compared with C. cUspar Liimarsson, from the Primordial rocks of 

 Vestergotland, it differs in being more pointed at the extremities and other- 

 wise of diff'erent outline, and also in having few or none of the transverse 

 rugse that so distinctly mark that species. From C. grenvillensis Billings 

 (Palseozoic Fossils of Canada, vol. i, page 101), it difi'ers in outline, in 

 having few or no transverse rugse or wrinkles, and in having a median 

 fuiTOW traversing its whole length instead of occupying only a part of 

 its length as the furrow does in that species. 



It is thought possible that the specimens of this sjDecies in the collec- 

 tion may have been denuded of rugae before they became imbedded, 

 because the surface of some of the slabs upon which they are found are 

 strewn with small bodies that resemble detached rugse. On the other hand, 

 such a supposition seems untenable, because some of those slabs are found 

 to contain both C. Linnarssoni and the following described species ; the 

 former being nude as usual, and the latter having- their abundant rugse in 

 place. 



■ The specific name is given in honor of Prof J. G. 0. Linnarsson, the 

 able Swedish geologist. 



Position and locality. — Tonto shale, probably of the Primordial period, 

 Grand Canon of the Colorado River, Mohave County, Arizona. 



Cruziana rustica White. 

 Plate I, iig. 1 a aud 6. 



Cruziana rustica White, 1874, Geog. & Geol. Exp. & Surv. west 100th Merid., Prelim. 

 Rep. Invert. Foss., 5. 



Body more or less elongated, flattened, more or less distinctly bilobed, 



the lobes being depressed-convex and the ends blunt ; median fmrow 



extending the whole length of the body and comparatively shallow thi-ough- 



;5 F 



