478 



LAMELLIBRANCH1ATA. 



slightly inequilateral, the hinge - line straight, without a 

 ligamental pit or teeth, and with no ears. Pseudomonotis 



(Eumicrotis), of the Car- 

 boniferous and Permian, 

 though in some respects 

 allied to Monotis, has a very 

 inequivalve shell, which is 

 hardly at all oblique ; while 

 the Silurian Amphiccelia is 

 more nearly allied to the 

 forms immediately to be 

 mentioned, the shell being 

 nearly equivalve, eared, 



and having a triangular cartilage-pit beneath the beaks. We 

 nrust also associate here the genera Anibonychid, and, provi- 

 sionally, Cardiola, both characteristically, though not exclu- 

 sively, Silurian, and the former leading us into the group of 

 Aviculidce represented by Pterinea and its allies. In Am- 

 lonychia (fig. 337) the shell is oblique, with nearly equal 



Fig. 335.Daonella (Halobia) Lommelli. Trias. 



Fig. 336. Pterinea (Avicula) demissa* 

 Lower Silurian. 



Fig. 337. Ambonychia rudiuta. 

 Lower Silurian. 



convex valves, winged posteriorly, the anterior ears being 

 nearly obsolete, and having the surface generally ornamented 



