518 



Forty-fifth Report on the State Museum. 



mary lamellse are usually broader and stronger than the remain- 

 der of the coil and may be preserved in the fossil state when the 

 rest is lost. These lamella?, near the middle of their length, give off 

 a pair of simple laminar processes which extend upward between 

 the bases of the cones, and usually unite. When these processes 

 thus unite the body formed is termed the jugum; * when they do 



Fig. 149.— Diagram of loop and spiral Athyris; x, spiral; a, primary lamellae; a , secondary 

 lamellae; a", umbonal blades; c, crura; I, jugum; e, lateral branches of jugum; s, saddle; 

 m, fimbriated extremity; t, stem of jugum; /,Jbranch c s of jugum; o, intercalary lamellae; 

 n, fimbriae on outer edges of spiral. 



not unite, as in Spibifeb, they may be called the jugal processes. 



The function of this jugum is, unquestionably, in part to 



strengthen the entire apparatus and resist the strains to which 



Fig. 150.— Zygospira modesta. The 

 brachidiura exposed by the removal 

 of the brachial valve, showing the 

 jugum. 



Fig. 151.— Jugum of Trematospira 

 nvulUstriata, attached to a por- 

 tion of the primary lamella'. 



the cones are exposed from gravitation and other causes. It is 

 therefore remarkable that Spirifer, in which the cones reach 



*This organ has usually been termed the loop, but the use of this term among the br.u-hiopods 

 with calcified spirals causes obscurity and confusion, as the word was originally applied to the 

 entire, brachial support in the terebratuloidfl, and it must continue to be used with this meaning 

 while the relations of the true loop to the jugum of spire-bearing shells is that of a whole to ■ 

 part. 



To 



