144 



SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I48 



<& <s> fi> <2> <2> 



B 



F G H 



Fig. 34. — Stenoscisma schlotheimi (von Buch), Permian, Possneck, Germany; 

 sections by Weller (1914, p. 109, fig. 1, C-K), X 3#. 



mens; costation variable, normally beginning at least 3 mm. anterior 

 to beaks, some adults nearly smooth, with only one or two weak costae 

 on anterior of fold, others with low rounded costae numbering up to 

 five (normally three) on fold, one fewer in sulcus, and up to six on 

 each flank: most specimens between these extremes, none strongly 

 costate ; growth lines weak, closely spaced ; growth laminae only 

 slightly stronger, more widely and irregularly spaced. 



Pedicle valve rather flat transversely, with geatest swelling just 

 anterior to umbo, greatest convexity longitudinally through sulcus ; 

 beak short, sharp, suberect to erect, with gently rounded beak ridges ; 

 delthyrium small, triangular, constricted by pair of small conjunct or 

 disjunct deltidial plates; foramen open, small, subtrigonal to slitlike; 

 posterolateral flanges long, broad, overlapped by edges of brachial 

 valve, normally completely covered. 



Brachial valve more strongly convex, greatest convexity trans- 

 versely, longitudinal profile along crest of fold only gently curved ; beak 

 bluntly angular, apex within pedicle valve. 



Pedicle valve interior with spondylium formed by junction of dental 

 plates, line of junction meeting floor along midline of valve in apex, 

 becoming elevated upon low median septum duplex somewhere beyond 

 1 mm. from apex ; height of septum increasing anteriorly, reaching 

 height near 1 mm., length of spondylium about one-third length of 

 valve. 



Brachial valve interior with camarophorium on short high median 

 septum, shallowly spoon-shaped, rather broad, beginning very near 



