458 CARBONIFKR<niS FORMATIONS AND KAUNAS ot COLORADO. 



1 liiivc [)l;ici'il Afiirc/i/'xd/i/d' iiinrcoukuKt in the y'ciius Worthtm.ia witli some hesi- 

 tation. It cloiirly l)oloiigs to the group of Pleurotouutr'nt^ iiiid is more nearly related 

 to Wortlwma than it is to Murchisonia. 



Localitii iiiuihorhon,. — San Juan region (stations 2340, 2345); Rico formation. 

 Leadville district (station 2275); upper portion of the Weber formation. 



WORTHENIA? sp. (t. 



This form was identified as Murchisonia sp. in the list of the Leadville mono- 

 graph," and it is too poorly preserved to be determined with certainty. Even its 

 generic position is a matter of doubt. It is one of those forms with a lofty spire 

 and very gradual taper. Its dimensions must have been 24 mm. in height, with a 

 proximal diameter of about 8 mm. The peritreme appears to have been carinated, 

 and I judge that its sj)ecitic relations are near the two species just di.scussed. 



Locality and horizon. — Leadville district (station 2275); upper portion of the 

 Weber formation. 



WORTHENIA ^ sp. ?y. 



This form is allied to the species which Geinitz '' described under the name of 

 MMTchi^onia nehraskeiisis, but it is certainly specifically distinct. It is much smaller, 

 as will appear from the fact that the entire height is onl}' about 2 mm. The width 

 is nearly half as much, and there are 6 volutions. It has therefore proportionally 

 a somewhat lower spire than M. neh'askensis, and the sutures are less oblique 

 to the axis. The shape of the peritreme is strongly arched but not subangular. 

 The surface of the final volution is crossed by four thin elevated ridges, which are 

 about equal distances apart. The upper one is near the suture, but the others are 

 disposed very much as in M. neiraskensis. The lower side of the peritreme is crossed 

 by several revolving ridges, which are less jsrominent than the ones above. While 

 there are four of the latter on the final volution, there are but three on that which 

 precedes it. 



I am by no means sure that this form possessed a slit band and its position with 

 the Pleurotomariidse is therefore uncertain. If this structure is really present it 

 probably occurs on the periphery between the two lower strong revolving ridges. 

 Even if it belongs to J'leurotojnaria, however, I am doubtful whether it should be 

 referred to the genus Worthenia. 



Looality. — Grand River region, Glenwood Springs (station 2193). 



aU. S. Geol. Surv., Mon., vol. 12, 1886, p. 70. 



b Carb. und Dyas in Nebraska, 1866, p. 12, pi. 1, flg. 17 



