DESCEIPTIONS OF SPECIES. 287 



Spieifer sp. a. 



The only material at present iu the collection which could have served as 

 evidence for the appearance of Spirifer rockyinontanus in the faunal list of the Blue 

 limestone given in the Leadville monograph," consists of two imperfect specimens 

 from station 2377. They are mere fragments of external casts, consisting of a 

 group of radiating strife, none of the liner ornamentation having been preserved. 

 From the curvature of the surface and the character of the plications I judge that 

 these impressions were made b}" a Spirifer. The species is most likely of the imhrex 

 t3-pe, as the latter is defined by Hall and Clarke. The sinus was very faintly 

 bounded and elevated, and contained, if its limits are correctly ascertained, four or 

 five plications. These are too fine and too numerous to afford much probability 

 that this foi'm is identical with Sj). rocJcyTnontanus^ Sp. heokuh, or Sp). increheseens, 

 and an exact identification is clearly impossible. The plications are no finer than in 

 a fine example of Sp. centronatim., such, for instance, as one of the impressions from 

 Larimer Count}-, but if really belonging to the Waverly species they are particularly 

 large specimens with plications unusually slender for the size of the shells. 



Locality and horizon. — Leadville district (station 2377); Leadville limestone. 



Spirifer sp. h. 



In the "Blue limestone" of the Leadville region, a small Spirifer is found, fre- 

 quently in considerable abundance. It is this form which appears in the faunal list 

 of the Leadville monograph as Spiriferi7ia sp. probablj' new, cf. Sp. hentxtckiensis."- 



The imfortunate preservation of this fomi renders it difficult of study, and its 

 generic position is still somewhat uncertain. It occurs in a matrix of chert and 

 therefore but little can be done in the way of manij^ulatiou. The shell substance has 

 been completelj' removed or is otherwise so altered that it can not be told whether 

 the structure was punctate or mei'ely fibrous. The cavity thus left has in many cases 

 been coated with a rusty or siliceous deposit, which often entirely obscures the 

 superficial markings. 



The shape is that of Spiriferina and of the Delthyrk group of ^pirifers. The 

 shell is transverse, semicircular. The cardinal angles seem to be rounded and the 

 hinge line is thus a little shorter than the width of the shell below. The area of the 

 ventral valve is rather high and incurved. The fold and sinus are moderately broad 

 and high, and are marked respectively by a median groove and ridge which can be 

 clearly seen in most specimens. The fold and sinus are otherwise simple. The sides 

 are marked by 5 or 6 simple strong plications. Large representatives of this species 

 have a transverse diameter of at least 24 mm. 



aU. S. Geol. Surv., Mon., vol. 12, 1886, p. 66. 



