Raymond — Common Devonian Brachiopods. 285 



phomena lepis Bron., of the Middle Devonian from Eifel, 

 Belgium, and the Asturias, were placed in this division. 



The development of the hinge structure, form of shell, and 

 convexity of valves is very similar in the three species (S. 

 incequi striata, S. perplana, and P. iowaensis) just described. 

 The points of greatest difference are : 



First: The Strice. — S. inceqvAstriata produces new striae by 

 implantation, S. perplana by both implantation and bifurca- 

 tion, while P. iowaensis has normally no strise at any stage of 

 development. 



Second: Muscle Scars. — S. incequistriata has a type very 



different from that of the other two, and in the ventral valve 



there is a change in the form of the muscles during the ephebic 



and gerontic stages. In the other two no such change has 



been observed. 



3 



Figure 3. — Stropheodonta junia Hall ; part of the muscle area of a ven- 

 tral valve, showing the anterior and posterior elements of the adductors, and 

 the pedicle muscle scar, x 3. 



Comparing the scars in the ventral valves of Stropheodonta 

 junia (figure 3), S. perplana, S. demissa, and Pholidostrophia 

 iowaensis, it is at once seen that they are very similar. In 

 each the diductors are broad, nabelliform, separated by a low 

 septum, and bounded on their posterior lateral edges by more 

 or less papillose ridges. Between the diductors are the elon- 

 gate scars of the adductors, two pairs in each case. In the 

 dorsal valves of S. demissa, S. perplana, and P. iowaensis, 

 there is more variation in the form of the scars, but it is a 

 variation in the form of the limiting structures rather than in 

 the shape of the scars themselves. In each, there are two 

 pairs of scars, one pair somewhat anterior to and between the 

 members of the other pair. In S. demissa and P. iowaensis 



Am. Jour. Scl— Fourth Series, Vol. XVII, No. 100. — April, 1904. 

 20 



