122 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. 53 



Page 



DESCRIPTION OF PLATE 9 



a<:. = apical callosity. h. = central muscle scars. 



cl. = cardinal muscle scars. s. = median septum. 



//>.= pseudo pedicle groove. t;.y. = vascular sinuses. 



Acrotreta ophirensis descendens, new variety 95 



Fig. I. Top, side, and back views of type specimen of ventral valve 

 from Middle Cambrian shaly limestones of the Weeks for- 

 mation, south of Marjum Pass, House Range, Millard 

 County, Utah. U. S. National Museum Catalogue No. 



521430- 

 la. Interior of an associated dorsal valve. U. S. National Mu- 

 seum Catalogue No. 52143^. 



Acrotreta niarjumensis, new species 94 



Fig. 2. Top, side, and back views of a ventral valve. U. S. National 

 Museum Catalogue No. 52116a. 

 2a. Interior of an associated dorsal valve. U. S. National Mu- 

 seum Catalogue No. 52116Z7. 



The specimens represented by Figs. 2 and 2a are from 

 the Middle Cambrian limestones of the Marjum formation, 

 south of Marjum Pass, House Range, Utah. 



Acrotreta ulrichi, new species 96 



Fig. 3. Top, back, and side views of type specimen of ventral valve 

 from the Middle Cambrian limestones of the Reagan for- 

 mation, east of Homer, Woods County, Oklahoma. U. S. 

 National Museum Catalogue No. 52180. 



Acrotreta bellatula, new species 93 



Fig. 4. Top, side, and back views of a ventral valve. U. S. National 

 Museum Catalogue No. 52072a. 

 4rt. Interior of a ventral valve. U. S. National Museum Cata- 

 logue No. 520726. 

 46. Cast of the interior of a dorsal valve. U. S. National Mu- 

 seum Catalogue No. 52072c. 



The specimens represented by Figs. 4, ^a-h are from 

 Middle Cambrian limestones of the Marjum formation, 

 south of Marjum Pass, House Range, Millard County, 

 Utah. 



Acrotreta rudis, new species 95 



Fig. 5. Type specimen, an exfoliated and crushed ventral valve from 

 Middle Cambrian shales, 3.5 miles (5.63 km.) from 

 Rogersville, on the road to Melindy's Ferry, Hawkins 

 County, Tennessee. U. S. National Museum Catalogue 

 No. 52111. 



Linnarssonella transversa, new species 92 



Fig. 6. Top and side views of type specimen of ventral valve from 

 Upper Cambrian shales of the Orr formation, south of 

 Marjum Pass, House Range, Millard County, Utah. U. S. 

 National Museum Catalogue No. 52201. 



