Raymond — Common Devonian Brachiopods. 295 



short distance, but toward the front of the shell they become 

 very numerous. 



Braohidium. — The smallest specimen retaining the brachid- 

 ium, and the only one in which the loop is complete, is about 

 4 mm in length. The loop extends about half-way to the front 

 of the valve. The primary lamellae run sharply upward and 

 forward, and the anterior portions run about parallel to the 

 floor of the valve, meeting at the front in an acute angle. As 

 the two lamellae approach each other they become wider, and, 

 where they join, there is also a point directed backward (figures 

 14, 15). This is evidently an immature condition of the loop 

 and differs greatly from the loop of the adult of this species. 

 It agrees with the centronelliform stage of loop as described 

 by Beecher and Schuchert.* This is the second genus of 

 brachiopods in which this stage of loop has been observed, 

 and its presence serves to confirm the view expressed in the 

 paper referred to, that the Centronella form of loop is a primi- 

 tive one for this superfamily of brachiopods. It differs slightly 

 from the loop of Dielasma tv/rgida\ in that the lamellae are 

 narrower and the angle in front is less acuminate. 



Cyrtina hamiltonensis Hall. 



(Plate XV, Kow 6.) 



Pal. N. Y., iv, 1867, p. 268, pi. 27, figs. 1-4; pi. 44, figs. 26-33, 38-52. 



Nepionic Stage. — The smallest individual in the collection 

 represents this species in the nepionic stage. The shell is 

 nearly circular in outline, and the length and breadth are the 

 same, — -53 mm (figure 16). The hinge line is -32 mm long and 



16 17 18 19 



Figure 16. — Cyrtina hamiltoneyisis Hall; outline of the smallest speci- 

 men, x 28. 



Figure 17. — A larger specimen ; profile, x 16. 



Figure 18. — The same ; outline, x 16. 



Figure 19. — A slightly older individual, showing the rapid change in the 

 relative convexity of the valves, x 16. 



nearly straight. The beaks of the two valves are elevated 

 above the hinge line, and between them is the pedicle opening, 

 which is shared by both valves. The valves are subequally 

 convex and smooth, with no trace of fold or sinus (figures 

 17, 18). 



* Proceedings Biol. Soc. Washington, vol. viii, p. 73, pi. x, fig. 1. 

 \ Loc. cit. 



