86 LUTRARIA.— MYA.— BYSSOMIA.— HYATELLA— SOLEN. 



extremities, and most of these animals live buried in the 

 sand or mud .; sometimes they excavate holes in stones or wood. 

 They are divided into Mya, Lutraria, Anatina, Glycymera, 

 Solemya, Byssomia, Hyatella, Solen, Psammobia, Pholas, Tere- 

 do, Fistulana, &c. 



12. The Lutraria closely resemble the Mactrse ; but their 

 hinge is unprovided with lateral laminae, and their valves are very 

 gaping, particularly behind, through which passes the thick fleshy 

 cylinder formed by their double tube. A large species is found 

 in the sand, at the mouths of several rivers in France. 



13. In the Myse there is a projecting plate in one of the valves 

 and a pit in the other, joined by a ligament ; the Anatin.e have 

 a small plate in each valve, giving attachment to a ligament ; 

 and the Solemy.e and Glycymera differ from the My.e in their 

 external ligament. 



14. The Byssomia, in place of living in the sand like the 

 preceding, penetrate stones and corals, and attach themselves to 

 them by the aid of a byssus. Their shell is oblong, without a 

 distinct tooth, and gaping about the middle of the inferior edge, 

 for the passage of the foot. 



15. The Hyatell.e have nearly the same general form; but 

 the tooth of the hin^e is more marked. 



t p 



Fig. 109. — SOLEN. 



16. The Solens, commonly called razor shells, knife handles 

 {Jig. 109), from the cylindrical and elongated form of their 



Explanation of Fig. 109. — c. the shell; — a. the anterior extremity of the 

 mantle ; — p. the foot ; — t. the tentacles. 



12. How is the genus Lutra'ria characterized ? 



13. What are the characters of the genus Mya ? 



14. What are the characters of the genus Bysso'mia ? 



15. How is the genus Hyate'lla characterized ? 



16. What are the characters of the genus Solen ? 



