ECIIINOCARIS. PPP. 7 



towards the dorsum, broad and convex towards tlie lower 

 portion, and occupying nearly one-half of the entire area. 

 Near the center of the limiting furrow and just anterior, is a 

 strong abruptly elevated node carrying the optic s]3ot, which 

 is usually marked by a slight depression on the summit of 

 the node. There is also a small node in each valve adjacent 

 to the dorsal line, near the posterior apex of the area. 



The thoracic portion of the carapace is marked by two 

 large tubercles, a long, sharp, doubly curved ridge, and a 

 row of small nodes along the dorsal line. One of these 

 tubercles is elliptical in outline, oblique, and situated near 

 the middle of the anterior end, back of the optic node. 

 The other elevation is elongate, with its longest diameter at 

 right angles to the hinge, and marked by a small subcentral 

 node. The ridge extends near the lower portion of the 

 valve, concave to the margin along the anterior half of its 

 extent, recurving and nearly following the contour of the 

 lower posterior mai'gin of the valve. 



One specimen has been observed which preserves the 

 mandibles in situ, and is represented in Fig. 16 of Plate 

 I. The mandibles are broad and gibbous on the anterior 

 portion becoming narrow below; furnished on their inner 

 edge with a low of denticles ; situated near the center of the 

 carapace, and are nearly one-third the length of the valves. 



Abdomen tapering towards the posterior. end, composed 

 of six exposed segments, having a total length of one-fourth 

 greater than the length of the carapace. The segments in- 

 crease in lengtli towards the posterior segment, which has a 

 length equal to two of the anterior segments, and is twice 

 as long as wide ; while the anterioi- somites have a gi-eater 

 width than length. The anterior dorsal mai'gin of each is 

 tlii(;kened and arched backwards ; the posterior margin is 

 furnished with fi-om four to six strong s})ines, which projec^t 

 over the articulation of the succeeding segment. On the two 

 anterior joints these spines are much shorter, ai)i)earing only 

 as nodes. The ventral side is without spines, but is fui-nished 

 with broad arti(Milating faces. These characters indicate a 

 great freedom of motion in the parts of tlie abdomen and ac- 

 count for the many i)ositions in wliidi this member is found. 



