194 AN INTRODUCTION TO THE STUDY OF FOSSILS 



not through one of the beaks as in the majority of other 

 brachiopods. 



Lingula anatina is a large species very abundant in the Japa- 

 nese seas. 



Glottidia pyramidata (Fig. 75, A), belonging to the Lingula 

 group, is very abundant off North Carolina on shoals exposed 

 at low tide ; it occurs from Chesapeake Bay to Florida. In its 

 normal condition, it lies with its shell half buried in the sand, 

 its anterior setae so grouped as to form three rude channels for 

 the entrance of water at the angles of the front of the shell and 

 for its exit at the middle. Each mantle is at the same time 

 raised into two folds, one upon each side of the median line of 

 the shell, thus aiding in the formation of these water channels 

 (see Fig. 75, B). The tentacles of the brachia are directed 

 towards these setal tubes, while the vigorous motion of the cilia 

 covering the tentacles causes the movement of the water. At 

 this time the two valves are separated vertically but not laterally. 

 Anteriorly they are open, but posteriorly as nearly closed as the 

 pedicle will allow. The sand is kept out of the buried portion 

 of the shell by the arrangement of the lateral setae vertical to the 

 plane of the valves, the setae from opposite mantles meeting tip to 

 tip. When disturbed the shell is quickly drawn down into the 

 sand through the contraction of its long pedicle, the lower end 

 of which obtains greater purchase by being sheathed in a tube 

 of sand grains cemented together by the mucus which it secretes. 

 This species does not live beyond a year. 



1. Examiae specimens on the demonstration table, noting 

 the elongate pedicle emerging from between the two valves. 



2. How long geologically has Lingula existed? 



3. Is either valve perforated by a pedicle opening ? 



4. What is the use of the long pedicle ? 



5. How does the animal get its food? 



6. What is the composition of its shell ? 



7. How do fossil Lingulae indicate the depth at which the 

 inclosing sediment accumulated ? 



