DESCRIPTIONS OF SPECIES. 333 



Both specimens attain a size unusual for G. crustula and must have had a 

 diameter of 25 mm. and a length proportional. The striae seem to be without orna- 

 mentation and are about 1 mm. apart on one specimen and 0.8 mm. on the other. 



Except for being of somewhat larger proportions these specimens are quite 

 similar to C. cmstula. In comparison with C. roejJeri, however, the only other 

 member of the genus known from the Upper Carboniferous, they are much smaller, 

 more tapering, and with strife which are at the same time more distant and ai'e 

 sigmoidally curved instead of nearly straight. 



Locality and lioynzon. — San Juan region (station 2239?); upper part of the 

 Hermosa formation. Grand River region. Grand River, 1 mile below Eagle River 

 (station 2190). 



ENCHOSTOMA Miller, 1896. 



Enchostoma sp. 



At a station in the Crested Butte region (station 2313) occurs in considerable 

 abundance an organism which I feel little hesitancy in referring to Miller's genus. 

 Specimens have the bluish color and shining phosphatic surface which are both 

 striking and distinctive. In occurrence they are much ilattened, and cross the 

 surface of the limestone blocks in ribbon-like strips whose edges are parallel. 

 No tendency to taper is apparent in the specimens studied, but at the same time 

 no specimens of any considerable length have come under my observation. The 

 breadth rarely exceeds 3.5 mm., and sometimes measures but 2 mm. 



Miller believes these oi'ganisms to be the remains of mollusks and allied to the 

 Conulariida3. Whatever be the affinities of Oonularia, I am convinced that 'those of 

 Encho&toiiia are with the polj'chffitous annelids. The tube, which is the only por- 

 tion of the organism yet discovered, affords but a slender support for a conclusion 

 upon this point, but a suggestive resemblance, if no more, can be pointed out 

 between the Paleozoic shells under discussion and the living genus Hyalinacea. The 

 latter inhabits a smooth, gently tapering, incomplete, cylindrical tube, composed of 

 chitinous material, from which that of Enchostoma differs chiefly in being more 

 massive and made up of phosphate of lime (?) in concentric laminse. 



Locality cmd horizon, — Crested Butte district (station 2313); Weber limestone. 



SPIRORBIS Lamarck, 1801. 

 Spirorbis arietina Dawson. 



1871. Spirorbis arietina. Dawson, Geol. Surv. Canada, Rept. Prog., 1866-1869, p. 14, fig. — . 

 Carboniferous: Near New Glasgow, Nova Scotia. 



The Colorado shells referred to SjjitvrMs arietina attain a rather large size for 

 the genus. They are sinistral, and composed of four or five turns, the fii'st two or 

 three of which are in contact, forming a rather high spire with a broad, deep 



