332 PALiEONTOLOGY OF NEW-JORK. 



however, the concentric lines of growth are visible, and in a still less degree the radiating strife. 

 The valve fig. 5 a is a young shell, and the radiating stria; are very conspicuous, while the- 

 lines of growth are still visible. The specimen fig. 5 b maintains nearly the same proportions 

 as fig. 4, and showing slight indications of radiating striae upon the interior, though in a less 

 desrrce than in fig. 5 a. 



In the young shell the wing is not so distinct as in the older individuals ; and in fig. 5 6, 

 this part of the shell is represented too large. 



Fig. 4. Cast of the left valve. 



Fig. 5 a. The interior of the left valve of a young shell. 



Fig. 5 h. The interior of the left valve of a full grown individual. 



Position and locality. In the Coralline limestone at Schoharie. 



(Collection of John Gebiiabd junior.) 



694. 14. AVICULA LIM^FORmS (n. up.). 



Pl. LXXV. Fig. b o, 6. 



Shell slighly oblique ; height much greater than the width ; anterior wing scarcely defined ; 

 posterior wing slightly extended beyond the width of the shell, and strongly wrinkled ; surface 

 marked by strong radiating plications, most of which continue undivided to the base ; con- 

 centric lines of growth conspicuous. 



The specimen fig. 6 a is a cast of the interior of the right valve, the posterior wing of which 

 is broken off : the plications are quite distinct and angular, being of less width than the spaces 

 between. In the specimen fig. 6 b, which is the interior of the right valve, the spaces between 

 the plications are nearly flat, and much wider than elevated folds of the exterior surface. In 

 this specimen also the posterior wing is imperfect. 



The aspect of fig. 6 a is unlike Avicula ; but in comparison, it should be recollected that 

 the wing in entire specimens is much more extended, and the figure should have been drawn 

 to show this character. 



Position and locality. In the Coralline limestone at Schoharie. 



(Collection of John Gebh-^rd junior.) 



Several other species of this class of shells have been found in this limestone, but they are 

 uniformly in the condition of casts, and often so much distorted by pressure and obscured by 

 weathering that they afford no very satisfactory information. 



