193 



straight beaks ; the hinge lateral, without teeth ; the liga- 

 ment marginal, linear, very long, and rather internal. Re- 

 cent and fossil. PI. vi. fig. 23. 



MalleacecR. A marginal, sublinear ligament, either 

 simple or interrupted by rows of teeth, or crenulae ; the 

 shell lamellous, 



1. Crenatula. A flat, lamellated, subequivalved, rather 

 irregular bivalve ; the hinge sublateral, linear; marginal, and 

 crenulated ; the crenulae in rows, callus hollowed into pits, 

 which receive the ligament ; no groove for byssus. Recent 

 and fossil. PI. viii. fig. 22. 



2. Perna. A subequivalyed, flattish bivalve, with la- 

 mellar texture ; the hinge linear, marginal, formed of trans- 

 verse, parallel, sulciform teeth, not penetrating, and between 

 which the ligament is inserted ; a posterior groove, rather 

 gaping, for the byssus, under the extremity of the hinge, 

 with callous sides. Recent and fossil. PI. viii. fig. 21. 



3. Malleus. A rough, subequivalved bivalve, generally 

 elongated ; sublobated at the base ; with small divaricating 

 beaks ; the hinge edentulous ; an oblong, conical small pit 

 under the beaks, traverses obliquely the ligamental groove ; 

 the ligament, which is short and almost external, is inserted 

 in the sloping depression in each valve. Recent. PI. vii. 

 fig. 5. 



4. Avicula. An inequivalved, fragile, rather smooth 

 bivalve ; the base transverse and straight, with produced 

 extremities and caudiform anteriorly ; the left valve notched ; 

 the hinge linear, with a tooth in each valve beneath the 

 beaks ; the ligamental area marginal, narrow and grooved, 

 not traversed by the byssus. Recent and fossil PI vii. 

 fig. 6. 



5. Jleleagrina. 



This genus differs from avicula in being nearly equal 

 valved, of a roundish square figure, with no hinge tooth, 



c c. 



