1892.] WILLIAMS — HINGED BRACHIOPODA. II5 



the Terebratulidje coil in a reversed direction from those of the cal- 

 cified spiral supports in the Spiriferida^. 



In studying out this problem the following facts were observed : 



According to the latest reported range of genera of Terebratu- 

 lacje, given by Davidson, (Lc. p. 353), the following genera have been 

 found in the Silurian : 



JVald/ieimia, Cenironella Billings, RenessellLEria and Lepiocalia 

 Hall. 



This includes the sub-family Centroficllince and the genus Wald- 

 hei77iia of the sub-family Terebratiilidce. 



The characters given for Centronellince are " Loop long, composed 

 of two ribbon-shaped lamellce with crurje, the lamellce uniting at 

 their anterior extremities, and a more or less developed vertical 

 lamellte rises between." (p. 353). The two spires of Waldhcimia, 

 W. iWa7aiiT>3i\. and JV. G/assiiDa.v., (Brit. Foss. Brae. Sil. Sup., Vol. V, 

 p. 76, 79) are both small forms from the Wenlock, the first from the 

 upper, the second from the lower beds. The characters of the brach- 

 ial apparatus of the former species were perfectly made out by Mr. 

 Glass, who, with Davidson, did so much to elaborate these delicate 

 internal structures of Brachiopods. 



The character which unites all these early genera of the Tere- 

 bratulidre is the long loop. (See figures i and 3.) 



Three genera of the Spiriferacas, reported from the lower Silu- 

 rian are characterized by a considerable extension of what Davidson 

 has called "the primary lamellae of the spiral coils." These are 

 Zygospira, in which the lamella are produced laterally and are con- 

 nected by a long bridge or cross-bar, Aiiazyga of similar form but the 

 bridge is attached near the front at the point where the first coil of 

 the spiral turns toward the ventral valve and upwards, and Hindella, 

 in which the departure between the primary lamellae and the bridge 

 was at the extreme front extension of the apparatus. (See figure 6.) 



The association of these facts led me, several years ago, to think 

 there was some natural relationship existing between the calcified 

 apparatus of the two families, and a year ago I expressed in my course 

 of lectures the belief that they were closely related, but the difificulty 

 of showing the way in which one form could result from modification 

 of the other was not removed. Coming again this year to the same 

 place in my lecture course I attacked the problem anew and this time 

 in a purely inductive way. 



I analyzed the two forms and found in each a thin calcified 



