EARLY DEVONIC HISTORY OF NEW YORK AND EASTERN NORTH AMERICA \gj 



mal of the species, but the variation may be interpreted as one due to the 

 protracted continuity of the simple plicated condition of infancy. 



Variant (2) senilis [pi. 40, fig. 16]. Occasional expressions occur 

 in which the fasciculation becomes well pronounced as a secondary con- 

 dition following the sharp plication of early growth but finally is obscured 

 or lost by rapid intercalation so that the peripheral surface carries a great 

 number of fine subequal radii. This expression doubtless represents the 

 extreme development of the specific characters beyond the point usually 

 attained in the normal growth of the' species. 



Variant (3) equal is [pi. 40, fig. 14, 15]. Again, in certain full 

 grown shells the primitive coarsely plicate stage is so early suppressed 

 as to be scarcely noticeable and fasciculation is at once inaugurated and con- 

 tinued throughout the shell growth. This is a very early assumption of 

 mature characters unaccompanied by evidences of senile growth in final 

 stasi'es. 



We have indicated thus the various expressions of Stroph. co n ti- 

 ne n s to show again what may be termed the plasticity of the shell, its 

 easy departure from a somewhat unstable specific t)'pe, such as we should 

 expect to occur in a center of rapid development and dispersion. It is 

 hardly necessary to state that these variant expressions pass into one another 

 and are to be regarded as permanent ontogenic phases rather than as stable 

 departures from the type. 



Localities. This species is very common in outcrops along the shore 

 at Fruing's where its varieties are also present. It also occurs at Indian 

 Cove. 



Strophonella ampla Hall 



Plate 37, figure 12 



Strop homena (Strophodonta) ampla Hall. N. Y. State Cab. Nat, Hist. 



10th An. Rep't. 1857. p. iii 

 Strophodonta ampla Hall. Palaeontology of New York. 1867. 4: 93, pi. 14, 



fig. la-i 

 Strophonella ampla Hall & Clarke. Palaeontology of New York. 1892. v. 8, 

 pt I, pi. 12, fig. 13-15 



A single external cast of the ventral valve indicates the presence of this 

 large species. It agrees closely with the type specimens from New York in 

 its coarse and angular plications and in the degree of reversion. A very 

 fine concentric striation is also present on both this and one of the type 

 specimens though this feature is not specified in either description or 

 illustration of the species. 



The close relation of this to the preceding forms is undeniable, specially 

 to the var. equiplicata in which the primitive condition is long con- 

 tinued. Were it not that a specific name had already been employed for 

 this expression in its isolated occurrence in more southerly province it would 



