﻿SYMPITYNOTA 48 1 



erally badly blurred. The genus seems to be naturally divisible 

 into three groups, which deserve subgeneric rank. The typical 

 Symphynotas, which are thin to subsolid with doubly-looped 

 beak sculpture and have tolerably well-developed laterals ; Las- 

 migona with strong, straight, barred beak sculpture and radial 

 plications on the posterior slope, and Pterosygna typified by the 

 old Margaritana coiiiplanata of l^arnes with heavy hinge, obo- 

 vate shell and strong, doubly-looped beak sculpture. Although 

 ihese three groups dififer much from each other, yet many 

 specimens may be found, which connect them. Occasionally 

 Symphynota costata is destitute of posterior plications and may 

 have fairly well-developed laterals, and I have before me a 

 heavy S. coinpressa with teeth almost exactly like those of 

 costata and I have seen specimens of S. complanata, which 

 were quite elongated. 



Key to species of Symphynota. 

 Shell solid. 



Obovate, or short elliptical, teeth very heavy. 



S. complanata. 

 Rhomboid, costate behind. S. costata. 



Shell thin to subsolid. 



Much compressed. S. compressa. 



Not compressed, large, dark. S. charlottensis. 



Long rhomboid, compressed, teeth well developed. 



S. decorata. 

 Subcompressed, shining, teeth rudimentary. .S'. quadrata. 

 Small, distinctly biangulate behind. S. neglecta. 



Not distinctly biangulate. S. tnridis. 



Subgenus Symphynota, s. s. 



Shell smooth, subsolid, shining, rayed ; teeth delicate ; lat- 

 erals compressed, moderately developed. 



Symphynota compressa Lea. 



Shell long rhomboid, subcomipressed or compressed, thin to 

 subsolid, somewhat inequilateral ; beaks low. usually flattened, 

 their sculpture consisting of numerous wavy, more or less 



