118 



two and gave rise to the striae that traverse this portion of the margin 

 of the valves. If so, the valves of Lingulella may have had much less 

 mobility than those of Lingula, and perhaps a different interpretation 

 should i>e given to some of the muscle scars of Lingulella whose office 

 and u-e are based on supposed analogues in the living genus Lingula. 



Muscular Muscle -^cars. Cardinal and pedicle muscles. There is great difficulty 



ventral 'valve. ^ n recognizing the imprint of the cardinal muscles ; in a few valves very 

 shallow round pits (g) on each side within the visceral cavity appear to 

 represent the cardinal muscle*. A little in front of the cardinal muscles 

 on the median line, is a small lozenge shaped depression, which is separated 

 by a low elevation fro n a small round pit, also on the median line, this 

 pit (p) perhaps marks the point of attachment of the sinews of the ped- 

 icle muscle. From this small depression the thickened visceral callus, 

 occupying the middle third of the valve, extends forward to the central 

 group of muscles. 



Centrals - These form, on each side of t 1 e front of the callus, a trian- 

 gular group, consisting in each of a large posterior triangular print (h} t 

 and two smaller an'erior muscles ; of these the outer (I) is a narrow trans- 

 vet se'tri.mguUr scar with the acute point of the triangle turned inward , 

 the inner print (k) is rounder than the outer and somewhat posterior to 

 it; it is obscure. 



Laterals Two lateral muscle scars are imprinted at the side of the 

 valve, near the hinge area. Of these the posterior and smaller, though 

 outer (i) in t'ie ventral valve, is supposed to mark the place of a trans- 

 median muscle, the anterior and large (j), is the principal lateral muscle 

 (unless the office of these two muscles is reversed). 



Circulatory Thn vascular system Along the lateral margin in the posterior half of 



the shell, the imprint of the vascular trunks is straight; they diverge 

 considerably and throw off numerous branches toward the margin of the 

 valve. At the mid-length of the valve the trunks begin to converge, and 

 on the outside throw off a few shore branches, directed forward. On the 

 inside of the trunks the branches are numerous ; at first they are trans- 

 verse, but farther forward the branches, especially in the central space, 

 turn forward toward the opening between the extremities of the main 

 vascular trunks. 



DORSAL VALVB. 



Cardinal area. This is unusually wide for a Lingulella, and is dis- 

 tinctly striated transversely, the striae arching forward in the middle; the 

 areal borders are narrow and mark a change in the course of the striae 

 that traverse the back edge of the valve. A slightly raised ridge, like 



