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NEW YORK STATE MUSEUM 



At their beginning they are not deeply separated from the beaks, but 

 from that point downward they are divided from the body of the shell 

 by a deep and moderately broad sulcus, in the bottom of which lies a 

 narrow, rounded ridge. The surface of these byssal expansions is striated 

 parallel to their outer edge by concentric lines continued from the body of 

 the shell. The anterior projection of the beaks toward the opening 

 suggests the characters which were ascribed by Beushausen to his genus 

 Prochasma, which however was based on a very different order of shells. 

 As to the structure of the hinge, no evidence can be ascertained from 

 delicate barite replacements except the total absence of articulating 

 processes. These valves are found not uncommonly in the shales still in 

 normal apposition along the linear ligamental margin behind the beaks. 

 This is well shown in several of the figures given herewith. Along this 

 short posterior line only was attachment of the valves effected. 



Species of this type are not wholly unknown in other manifestations of 

 the Intumescens fauna. Posidonia hians Waldschmidt from Wildun- 

 gen ' is a closely related shell, and we are disposed to regard certain valves 

 from the black limestones in the Domanik of Timan, described and figured by 

 Holzapfel 2 as possibly of crustacean nature, as unquestionably appertaining 

 to this genus. Of the three figures given by Holzapfel all show the sicae 

 extended forward in the plane of the valves and two of these we have 



inserted here for comparison. They are described as 

 /AH? ( '••■ ver ) tenuous, fragile and depressed convex bodies. 



vfyS The author has not specifically designated these valves 

 - ' ^^ which now assume special interest from the concur- 



rence of the genus they represent in widely separated 

 localities. We therefore suggest the name Ptero- 

 c h a e n i a u c h t e n s i s. 



Fig. 8 Pterochaenia 

 uchtensis Timan (after 

 Holzapfel) 



'Waldschmidt, Zeitschr. d. deutsch. geolog. Gesellsch. 1885. p. 924, pi. 40, fig. 4; 

 Freeh, Devon. Aviculiden. 1891. p. 72, pi. 14, fig. 13. 



2 Die Cephalopoden des Domanik im siidlichen Timan, Memoires du Comite Geolog. 

 St Petersburg. 1899. v. 12, no. 3, p. 53, pi. 9, fig. 17-19. 



