MARCELLUS LIMESTONES OF LANCASTER 159 



observed. It becomes extremely abundant in bed I of the lime- 

 stone series and is common in all the other limestone beds, but 

 has not been found in beds F, G, and H, of the overlying shales. 

 The specimens in the lower shales are small but are character- 

 ized by the great length of the cardinal spines (fig. 4). Indi- 

 viduals having exceptionally long spines are not only smaller 

 but usually have also fewer plications. A specimen of average 

 proportions in bed C is 5.4 mm long, 6.8 mm wdde, and bears 22 

 plications. In bed I the majority of the shells are smaller than 

 in the shales, but in beds II and III there is a perceptible 

 increase in the average size of the specimens. The largest shell 

 which could be referred to this species occurs in bed VI. It is 

 9 mm long, 10.4 mm T\dde, and has 20 plications. The single 

 cardinal spine which is retained is nearly parallel with the hinge 



line. 



Chonetes lepidus Hall 



Pal. N. Y. 4:132, pi. 21 



This is a rare species in the limestones, only two well preserved 

 specimens having been found in bed VIII, but it becomes abun- 

 dant in the shales immediately overlying the limestone. The 

 plications on specimens from this locality are slightly less promi- 

 nent than on those from the Hamilton shales. 



Chonetes scitulus Hall 

 PI. 9, fig. 4-6 



Pal. N. Y. 4:130, pi. 21 



In bed III a single well preserved individual of this species 

 was found, but it is common in beds IV and V. 



Associated with shells of the normal form and size are others 

 which have been referred with doubt to this species. The shells 

 are slightly transverse, the largest specimens somewhat less so 

 than the smaller, and the hinge line equals the greatest width 

 of the shell. The ventral valve is moderately convex with often 

 a faint sinus along the median line which is traceable about two 

 thirds the length of the shell, but disappears before reaching the 

 margin. The dorsal valve has a concavity less than the con- 



