V MOLLUSCOIDEA — BRACHIOPODS 187 



secrete the dorsal and the ventral valves of the horn-like, em- 

 bryonic shell {protegulum, Fig. 73 h, G,H,I). About the same 

 time a crescentic fold, the future lophophore, grows out from 

 the inner side of the brachial mantle lobe, developing gradually 

 into the two arms which diverge from the mouth ; simultaneously 

 the muscles develop, the additions to the shell become calcareous 

 and in all ways the animal approaches the adult. 



1. Examine specimens, noting pedicle, mantle, adductor 

 and diductor muscles ; the relation of mouth to food grooves on 

 lophophore. 



2. Sketch transverse section of one of the brachia, labeling 

 food groove and tentacles. 



3. Make drawings of (a) entire shell, side view, (b) interior 

 and exterior of each valve. Label pedicle and brachial valves, 

 pedicle opening, teeth, sockets, cardinal process, brachidia, 

 adductor and diductor muscle scars. 



4. Sketch an ideal longitudinally transverse section through 

 the slightly gaping valves, labeling the valves, pedicle opening, 

 cardinal process, muscles and mantle. 



5. How are the valves held together? How are they 

 opened ? How^ closed ? 



6. Give the habitat of Terebratulina septentrionalis. 



7. What does the animal eat? How does it procure its 

 food? 



8. Briefly describe its digestion ; absorption ; circulation. 



9. How is the digestive waste thrown off ? 

 ID. How does the animal breathe ? 



11. What is its nervous system like? 



12. Describe the development of an individual from the fer- 

 tilized egg to adulthood. 



General Survey of Class Brachiopoda 



Marine animals, secreting a bivalved, equilateral, inequivalved 

 shell, which is composed of lime carbonate, lime phosphate, or a 

 horny substance (ceratin) ; the valves are dorsal and ventral 

 in position. The animal, in its youth, is always attached to a 

 foreign object by a posterior, fleshy stalk, called the pedicle; 



