﻿24 Bulletin 20 102 



The presence of this coral in the Jefferson limestone supplements 

 in an important way the evidence afforded by the Devonian 

 fossils as to the age of the lower portion of the Jefferson. As 

 previously stated, the Devonian fauna contains none of the 

 fossils commonly considered diagnostic of the Lower Devonian, 

 but the occurrence in the lower part of the Jefferson of Halysites 

 catenulatus affords stronger evidence of a horizon earlier than 

 Middle Devonian than would even the most characteristic early 

 Devonian species. If the validity of this evidence be con- 

 ceded, then we must conclude that both the Lower and Middle 

 Devonian are represented by the Jefferson limestone. 



Description of the Fauna 30 . 



CtELENTERATA 



Stromatopora sp. 



One or more species of this genus are rather common in the 

 Jefferson limestone. The character of the rock inclosing them is 

 not such as to preserve the minute structures sufficiently well to 

 determine the species. 



Locality: — Sixteen P. O. and Princeton, Montana. 



Favosites cf. limitaris Rominger. 



PI. I fig. 2. 



A form apparently closely related to this species is one of the 



most generally distributed fossils in the Jefferson limestone. It 



occurs generally, however, in a very poor state of preservation, 



making specific identification uncertain. 



Locality: — Princeton, Philipsburg, Logan, Sixteen P. O., 

 Montana; Paradise P. O., Utah. 



Spirorbis sp. 

 PI. I fig. 1. 

 Specimens of this minute shell occur on the surface of a 



30 The types of the new species described in this paper belong to the 

 collections of the U. S. Geological Survey. 



