Raymond: Fauna of Upper Devonian of Montan.a. 145 



also very different from the Devonian shell here described. The 

 Mississippian form should probably be known as Cleiothyridina sub- 

 lamellosa (Hall) as Schuchert has already suggested in '* Bulletin U. 

 S. Geol. Survey," No. 87, p. 183, 1897. He says: "American 

 specimens usually referred to this species are constantly smaller and 

 are often without sinus or fold. If these differences are of sufficient 

 importance to distinguish American specimens from typical Cleiothyris 

 roissyi, then this species should be known as C. sublat?iellosa Hall." 



From this Mississippian shell our specimens differ in their more 

 transverse form and in the deeper sinus in the ventral valve. 



The specimens of Cleiothyridina devofiica are very well preserved 

 and the great number of specimens in our collection exhibit a wide 

 range of variation. In young stages the shell is subcircular in outline, 

 becoming quite transverse and somewhat quadrate in the adult, while 

 old shells show a tendency to regain the circular form. The history 

 of the development of the sinus of the pedicle valve is similar. 

 In young shells it is entirely absent. In the adult it is strongly 

 developed, but in many old individuals it is practically ob- 

 literated. Individuals are found in which the development of one 

 or both of these characters is retarded or accelerated. Thus there 

 are small shells, especially in the red shales, with the deep sinus of the 

 adult and the subcircular outline of the young and other specimens 

 with the outline of the adult, but lacking the sinus. 



Locality. — This is a common shell in most of the zones of the Three 

 Forks shale of the Upper Devonian at Three Forks and Logan, 

 Montana. 



Subkingdom MOLLUSC A. 



Class PELECYPODA. 



Order PRIONODESMACEA Dall. 



Family PTERINEIDyE Dall. 



Genus Loxopteria Freeh, 



Loxopteria holzapfeli sp. nov. 



(Plate V, figures 1-7, 11.) 



Cf. Aviciila dispar Sandberger. " Versteineriaigen des reiiiischen ScJdchtensys- 

 t ems in Nassau,'' p. 284, t. 29, tig. 14. 



Cf. Kochia {^Loxopteria) dispar Freeh, 1891. ^^ Die devonischen Avictiliden 

 Detitschlauds ; Abhandlungen zur geologischen SpecialliaJtevon Preussen itnd den 

 ThUringischen Staaien," Band IX, Heft 3, p. 77, t. 6, figs. 4-4//. 



