40S OARBONTinCROlTS FOKMATTONS AND KAUNAS OF COLORAnO. 



Athi/ris orMculariK," Swallow doscribod iSj/ir/c/tm, iiiisKoirrienslN^ hiiHiiij;' his doscription 

 upon what I fool conlidont was the sumo t3'po of shell. The reasons for this oonelusion 

 are as follows: 



Mc(/hosney states tliat his siioll is olosoly allied to Ailiijrix KiMamellosa Hall, 

 and that it had sometiiues been referred to Terehratula pianos ulcata of Phillips. Both 

 the speeies mentioned belong to the Cleiothyris group of Ath/rin, and, as the general 

 character of the description indicates the contiguration and surface ornamentation of 

 Cleiothyris, it is practically certain that At hi/ /'in orMcidaris belongs to that group. 

 Furthermore, I find in the collections of the U. S. National Museum a species of 

 Cleiothyrh which bears Worthen's identification with 01 . arhlcularls, and at the 

 same time permits McChesney's description to be applied to it. 



Swallow's description of Sjnrigera missowriensis would of itself lead one to 

 infer that he had in hand shells of the Cleiothyris type, and such an inference receives 

 corroboration from the circumstance that it is said much to resemble 01. hirsiota Hall. 

 To be sure, it is said to differ from that species in being ornamented with lamellas 

 instead of the spines, which are, of course, a distinctive character of Cleiothyris., but 

 the lamella are described as imbricating, transversely costate, and as leaving gran- 

 idar ridges in falling off, details all of which indicate that the lamellae were spinif- 

 erous. It is true, also, that the structure is described as punctate, but the same 

 character is ascribed to several species of Seminula described under the names of 

 Spirigera charitonensis and 8p: hawni. Furthermore, among the museum collec- 

 tions are specimens of a Cleiothyris from Chariton County, one of the localities cited 

 by Swallow, which answer to his description in most particulars and yet clearly 

 indicate the subgeneric group to which they belong. 



The descriptions of CI. orhicularis and CI. missouriensis certainly indicate closely 

 similar shells, and the specimens in our collections which seem to best represent each 

 of those species I would feel no hesitation in referring to the same. Indeed, I find 

 it impossible to discriminate between the Pennsylvanian representatives of Cleiothyins 

 that have come under mj' observation, and must refer all to a single species. These 

 facts, and a consideration of the narrow limits of variation habitually shown in Cleio- 

 thyris as a whole, lead me to regard CI. orbicularis and CI. missouriensis as one and 

 the same species. 



It is probable that the Upper Carboniferous form from Brazil which Derby 

 identified with CI. sublamellosa Hall can be referred to this species, though the 

 South American shells attain a somewhat unusual size. It seems pretty certain that 

 the shells from Nebraska which Geinitz identifies as Athyris planosulcata also belong 

 here, and those from the west referred by White to the same species, after an exami- 

 nation of his specimens, I do not hesitate to add to this synonymj'. 



aMcChesney's publication was reTiewed in the Am. Jour. Sci. for March, 1860. Swallow's paper was presented for 

 puhlication in the St. Louis Acad. Sei. on July 2d of the same year. 



