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PilLJEONTOLOGY OF NEW-YORK. 



PLATE LXXX. Fig. la-e. 



Fig. 1 a. The anterior half of a large individual, preserving the shell. The line continued, marks 



the outline of the entire valve. 

 Fig. 1 b. View of the anterior extremity, showing the umbones, and a part of the dorsal margin ; 



below the umbones : where the shell is broken away, is shown the position of the 



muscular impressions extending deep into each valve. 

 Fig. 1 c. The dorsal side of the same specimen. 

 Fig. 1 rf. A fragment of the left valve of another specimen. 

 Fig. 1 e. Dorsal view of a cast of this species. 



PLATE LXXXI. Fig. Iffl-/. 



Fig. 1 a. Cast of a large individual, presenting the ordinary characters of specimens when not 



distorted. 

 Fig. 1 b. A cast of a much shorter specimen : probably the form is in part due to pressure on the 



posterior end. 

 Fig. 1 c. View of the anterior extremity of the specimen 1 b. 

 Fig. 1 d. Dorsal view of the same. 

 Fig. 1 c. A cast of a specimen somewhat distorted by pressure, which has projected the lower 



anterior end beyond the beaks above. 

 Fig. 1 /. View of the anterior end of the specimen fig. 1 e. 



Although the lateral views of the several specimens present considerable difference, there 

 seem to be no characters by which they can be distinguished ; and the figures on the following 

 plate show still farther the variations due to pressure. 



PLATE LXXXII. Fig. la-/. 



Fig. 1 a, b, c. Lateral views of casts, showing degrees of distortion. 



Fig. I d. A dorsal view where the umbones have been depressed, leaving the space between 



them projecting. 

 Fig. 1 e. Dorsal view of a cast, where the umbones have been pressed forward much beyond their 



natural relation. 

 Fig. 1 /, g. Anterior and lateral views of a small specimen, preserving the shell. 

 Fig. 1 h. The interior of a part of the left valve, showing the deep large muscular impression 



and the two smaller pits above, with the folds on the thickened portion of the shell. 



The groove beneath the umbo is likewise seen in the figure. 

 Fig. 1 2. The left valve of a specimen having the shell broken away, showing the numerous 



distinct laminte of which it is composed. The deep muscular impression is well shown, 



extending from the base at the anterior extremity upwards beneath the umbo. 



Position and locality. In the limestone at Gait, Canada West. 



