ASIPHONIDA. 



489 



shortest side. The hinge has numerous teeth on each side of 

 a central internal cartilage-pit. The Palaeozoic shells referred 

 to Nucula probably belong to other genera. Many species, 

 however, are known from the Secondary and Tertiary rocks. 

 Allied to Nucula is the characteristic Silurian and Devonian 



Fig. 351. Nucula bivirgata. Gault. 



Fig. 352. Tellinomya contracta. 

 Lower Silurian, a, Interior of right 

 valve ; b, Exterior of the same. 



genus Tellinomya ( = Ctenodonta of Salter). In this genus the 

 posterior side is usually, though not always, the shortest, and 

 there is an external ligament. The hinge is furnished with 

 numerous small teeth (see fig. 348, B, and fig. 352). 



Lastly, we have the group of shells included under the 

 head of Nuculanidce, which should probably form a family 



Fig. 353. Types of Nuculanidce. A, Interior of valve of Nuculana (Leda) lanceolate Plio- 

 cene ; B, Cucullella ovate Upper Silurian ; c, Yoldia striatula Cretaceous, enlarged ; D, In- 

 terior of left valve of Yoldia myalls Pliocene. 



by themselves, and which are distinguished from the pre- 

 ceding groups by having the shell more or less produced 

 posteriorly, and by the fact that the pallial line is usually 

 more or less sinuated (fig. 353, A). In Nuadana, or as it 



