BRACHIOPODA. 



677 



The type-species of Stringocephalus is the well-known 6". Burtini 

 of the Middle Devonian of Europe. In this well-known species 

 (figs. 547 and 548) the shell is sub-orbicular, with a prominent beak 

 to the ventral valve, and often growing to a great size. There is a 

 large foramen below the beak of the ventral valve, which is triangular 

 in the young shell, but ultimately becomes oval and reduced in size 

 by the growth of the deltidium. The ventral 

 valve has prominent teeth, fitting into corre- 

 sponding sockets (/) in the dorsal valve. The 

 cardinal process (J>) in the dorsal valve is very 

 prominent, and its free end is bifurcated to 

 receive a well-developed median septum (v) in 

 the ventral valve. A corresponding, but much 

 smaller septum (d) is present in the dorsal valve. 

 The hinge-plate (h) of the dorsal valve gives 

 origin to a large brachial loop (/), consisting of 

 two crura (c) which are reflected backwards about the middle of the 

 valve, and then, bending forwards, give origin to a wide ribbon- 



Fig. 548. — Stringoce- 

 phalus Burtini — Devon- 

 ian — reduced in size. 



Fig. nq.— Thecidium papillatum. e, Hinge-area; n, Hinge-teeth of ventral valve 

 r r, Granulated border of the interior of the dorsal valve. Cretaceous. 



shaped band, which is sub-marginal in position, and gives off radiat- 

 ing shelly processes along its inner margin. 



Family 10. Thecidiid/E. — In this family the shell is usually 

 fixed to the sea-bottom by the substance of the beak of the ventral 

 valve ; the arms are united in the form of a bridge over the visceral 



