248 NEW YORK STATE MUSEUM 



But this close similarity may be due to a possible derivation of both 

 from S. p e t i 1 u s of the Waldron area.^' 2 



S. cyclopterus Hall 

 The young of this species is quite similar to S. vanuxemi in 

 external form and markings. A young specimen of S. cyclop- 

 terus from the Coe3mians gives the following measurements : 



fe o M ^ ^ 



Oh .-1 o o 



o w a S ^ Q 



W ■ 



H 



H 



Q 







< 



^ 



W 



W 



e^ 



J 



PQ 



« O 



« O 



o w « § < < 5 



^ k1 W p U W O) 



2.5 4.5 1.8 3 Brachial valve 



5 9 1.8 4 Pedicle valve 



In the above brachial valve, the central plication or fold is very 

 slightly larger than those on each side of it; and the plications are 

 but slightly wider than the furrows between them. No flattening 

 of the fold was noticeable. The sinus of the pedicle valve near the 

 umbo is but slightly wider than the furrows on each side, while at 

 the front of the shell it is about twice as wide. All this is also true 

 of S . vanuxemi. This young specimen also agrees with 

 S. vanuxemi in the number of plications but exceeds it in the 

 proportion of length to breadth of the valves. With the exception 

 of this last fact, the similarity between the two species is almost 

 perfect and suggests a possible derivation. ^ 



In many of the New Scotland beds occur frequently only the 

 internal molds of S. cyclopterus. They bear a general 

 resemblance to S . m u r c h i s o n i but the cast of the muscula- 

 ture of the pedicle valve of the former is narrower and the sinus in 

 it is not as wide as in the latter species. The internal mold of the 

 plications is also usually less pronounced in the former. The surface 

 of the mold on both sides of the muscular impression is papillose in 

 both species, indicating a punctate surface on the corresponding parts 

 of the shell. 



'Grabau. N. Y. State Pal. An. Rep't 1902, p. 1046. 

 ^'Clarke & Beecher. N. Y. State Mits. Mem. i. 1889. p.7S. 

 'Stuart Weller [Geol. Sur. N. J. 3:287] calls attention to the likelihood 

 of the derivation of S. cyclopterus from S. vanuxemi. 



