466 PROCEEDINGS: BOSTON SOCIETY NATURAL HISTORY. 
The suture is short and curved, not readily resolvable into a zigzag 
of lines. Coming across the posterior rim of the depressed area as a 
line passing away from the median plane to one side, it then suddenly 
bends to the opposite side across the median plane and then down the 
depressed area along its posterior boundary far to one side to disappear 
under the lateral elevated rim of the depressed area. 
The floor of the depressed area is chiefly a transverse ridge or tongue 
that passes across the median plane parallel to the suture and likewise 
disappears under the elevated lateral rim of figure 41 (pi. 48). This 
transverse tongue goes from the posterior rim of the annulus on one 
side far over to the opposite side of the annulus. It is marked off 
posteriorly by the transverse part of the suture and anteriorly by a 
wider groove. The deepest part of the depressed area is far to one 
side. 
The color of the annulus made it noticeable. It was often reddish 
yellow and posteriorly greenish while -the central tongue was white, 
but there were many individual differences. 
The annulus was well calcified except that the bottom of the median 
anterior groove and also the groove along the anterior edge of the 
transverse tongue were thin and translucent. On each side of the 
anterior face far from the median groove there was also a thin and 
partly calcified area. 
The dorsal aspect of the exoskeleton (pi. 48, fig. 42) shows the 
trumpet tube passing very far to one side and lying near the posterior 
edge of the annulus in correspondence with the like position of the 
external suture (pi. 48, fig. 41). Though this figure fails in showing 
it, the anterior face of the annulus rises up above the general level so 
as to form a wide angle with the rest of the annulus and being about 
half the entire length of the annulus the appearance might be com¬ 
pared to a small ‘wall pocket’ in which the posterior part of the 
annulus juts out from the anterior half as a pocket holding the 
trumpet tube in it. 
The trumpet tube, followed from its posterior end where it is nearly 
median, turns abruptly to one side and runs transversely. It is this 
part only that is at all conspicuous as it stands up above the adjacent 
parts so that it shows from the posterior view (pi. 48, fig. 44) against 
the background furnished by the low-hanging anterior face of the 
annulus. Then, far from the median plane, the tube becoming more 
and more depressed, turns back as a second bend and sinking into the 
general level of the exoskeleton, approaches the median line again. 
