LAMELLIBRANCHIATA. 371 



group, in Schoharie and Otsego counties, and found in nearly all localities 

 througiiout Eastern and Central New York, but seldom in the softer shales in 

 the western part of the State. It also occurs in the shales of the Hamilton 

 group at Patterson's creek, Va. 



Grammysia lirata. 



[ Probably the young of Grammysia alveata. ] 



PLATE LIX, FIGS. 6-12. 



Orammynia lirata. Hall. Prelim. Notice Lamellibranchiata, 2, p. 57. 1870. 



" " Pal. N. Y., vol. V, pt. 1. Plates and Explanations : PI. 59, figs. 6-12. 1883. 



A farther e.vamination of this form, with larger collections, indicates that 

 the characters upon which the species was founded may be only those belong- 

 ing to an immature shell. 



In these forms the concentric undulations are comparatively more numerous, 

 and are not so distinctly limited by the umbonal ridge. The numerous 

 and characteristic concentric folds are shown in figs. 6, 7 and 10 of plate lix. 

 The ridge adjacent to the escutcheon, as shown in fig. 10, is due to the vertical 

 compression of the shell, and does not differ from the same part of the shell in 

 G. alveata when preserved in similar conditions. The same figure shows the 

 concentric undulations extending over the cardinal slope in a subdued degree, 

 not limited by the umbonal ridge. In figs. 8, 9 and 11, the concentric folds 

 pass over the umbonal slope in a subdued condition, and are not anywhere 

 abruptly terminated by the umbonal ridge as in characteristic specimens of G. 

 alveata. In form and other characters these specimens do not differ from that 

 species. 



This form is more abundant than any other in the Hamilton group, and is 

 perhaps subject to greater variation from compression than any other of the 

 genus. When occurring in what appears to be its normal condition, the shell 

 is much longer on the posterior end ; but many of the individuals in the collec- 

 tion have been so distorted as to leave this part of the shell not more than half 

 as long as the anterior end. The same degree of distortion is liable to occur in 

 the height or depth of the valves, so as to produce an almost endless variety 

 of form. 



This species occurs in all the localities cited for G. alveata. 



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