MOLLUSCOIDEA — BRACHIOPODS 



197 



1. Sketch the cut portion of a vertical sec- 

 tion through the entire shell from beak for- 

 ward, labeling the pedicle and brachial 

 valves. 



2. How do you distinguish this genus from 

 Rafinesquina ? 



3. Was the pedicle valve concave and the 

 brachial convex in its youth as it is in its 

 adult state ? Reasons. 



Leptaena (Fig. 79). 



Ordovician-Mississippian. 

 Pedicle valve convex, brachial concave. 

 The flat portion of the shell is concentrically 

 wrinkled; where these wrinkles cease the 

 shell is abruptly deflected. Shell with closely 

 appressed valves, thin, i.e. with very little 

 space for the soft parts of the animal. Shell 

 punctate. 



I. Sketch {a) a view of exterior of pedicle 

 valve showing the concentric wrinkles and 

 the deflected anterior portion, ih) the cut 

 portion of a vertical section through the entire 

 shell from beak forward. Note pedicle and brachial valves 



Fig. 78. — A diagram- 

 matic longitudinal 

 cross section of the 

 brachiopod shell. 

 Strophomena pla- 

 numbona Hall ( X 2). 

 Section cut beside 

 the deltidium. This 

 is similar to Rafines- 

 quina (Fig. 77), ex- 

 cept that the con- 

 vexity of the valves is 

 reversed ;b., brachial 

 valve ; c.a., cardi- 

 nal areas of brachial 

 and pedicle valves; 

 h.L, hinge line; p., 

 pedicle valve. 



A B C 



Fig. 79. — Leptcena rhomhoidalis Wilckens. A, adult brachial valve (natural size), 

 showing the exceptional retention of the pedicle opening ipe.o.) in the opposite 

 (pedicle) valve. B, adult pedicle valve. C, pedicle valve ( X 10), a young stage 

 in the growth of the shell showing the beginning of the radiating striae. C redrawn 

 from Beecher. (A and B after Hall and Clarke.) 



