GIRTY, GEOLOGIC AGE OF THE BEDFORD SHALE 3H 



These two forms present serious difficulties of exact identification, 

 being complicated with each other and with the two terebratuloids which 

 I have called Crancena aff. siibelliptica and Cryptonella ? sp. These are 

 among the rarer forms of the Bedford fauna. When preserved in the 

 shale they are apt to be badly crushed, but they often retain the shell, so 

 that its structure can be determined. When preserved in the calcareous 

 nodules, the shell is not retained (or its structure is obscured), but the 

 proportions are not seriously altered. Thus, among these poorly charac- 

 terized, generally ovate forms there are clearly two types, one with a 

 punctate and one with a fibrous shell and of each type there appear to be 

 two species, distinguished more or less strongly by size and configuration. 

 Where the specimens have their real characters obscured by crushing or 

 in other ways (and this is true of many of them) they cannot be satis- 

 factorily placed in this scheme. The shells with fibrous structure have 

 the general appearance of Athyroids, and for such they might casually 

 be mistaken, but the ventral valve (and in one type both valves) is fur- 

 nished with a well-developed median septum. This character is not only 

 alien to the Athyroids, such as Composita which the configuration sug- 

 gests, but I do not know of any Carboniferous genus which has at once 

 this shape and this structure. The larger of the two species suggests 

 Camarospira more than any other genus with which I am acquainted, 

 and the smaller more transverse one, which has a dorsal as well as a ven- 

 tral septum, is certainly very suggestive of Nudeospira. I have even 

 observed what appear to be traces of fine setae on external molds. 



It cannot be positively asserted that these forms belong to the genera 

 named, but it is true so far as I am aware that no genera having the 

 character of these Bedford shells are known in any Carboniferous rocks 

 of the Appalachian region. A few occurrences of Delthyris and Nudeo- 

 spira have been noted in the Kinderhook group of the Mississippi Valley, 

 but aside from this the Pholidops, the Delthyris, the Nucleospira ? and 

 the Camarospira ? are peculiarly Devonian types and are not found in 

 the Carboniferous. 



On the other or Carboniferous side must be mentioned the Syringo- 

 thyris, which can, however, no longer be regarded as distinctly Carbon- 

 iferous in its generic range. The Bedford form is, however, identified 

 with a Carboniferous species. Again, I have a single very poor Spirifer 

 which seems to belong to the marionensis group (a Carboniferous type), 

 but which may be a somewhat abnormal S. dis functus (a Devonian type). 

 Lastly there is a species of Pholadella which is more nearly allied to the 

 Carboniferous P. newberryi than to the Devonian P. radiata. These 

 Carboniferous affinities, it will be noted, are specific, while the Devonian 

 ones are generic. 



